Don’t get us wrong. There’s nothing we like more than a position that makes us money. And that’s exactly what our favorite master limited partnerships (MLP) are doing now.

But sometimes the wise thing to do is to take some money off the table, particularly from a big winner that seems to be running on euphoria. That’s what we’re doing this week with Aggressive Portfolio holding Navios Maritime Partners LP (NYSE: NMM).

At a time of intense uncertainty about the market, the economy, and taxes, well-placed energy MLPs certainly are more attractive than ever. And the best are using their good fortune to issue unprecedented amounts of low-cost capital, financing accretive acquisitions and construction and ensuring many more quarters of rising distributions.

More than anything else, it’s those rising distributions that ensure our MLPs’ unit prices will continue to rise over time. As the past couple years of trading show, even the best MLPs can be volatile as investor sentiment for them waxes and wanes. Over the past year that’s been an unabashed positive for the group, just as it was a negative in late 2008.

Eventually, however, unit prices follow distribution growth. And given today’s low cost of capital and the wealth of opportunity to buy and build new assets–particularly to serve fast-growing shale gas areas–there’s a lot more of that ahead.

Growth opportunities in basic infrastructure never flagged during the recession and appear to be accelerating now. Already in April, for example, Conservative Holdings Enterprise Products Partners LP (NYSE: EPD) and Kinder Morgan Energy Partners LP (NYSE: KMP) announced major new expansion moves in shale gas.

Kinder’s actually took place this week, with Chairman and CEO Richard Kinder announcing the purchase of 50 percent of Petrohawk Energy Corp’s (NYSE: HK) natural gas gathering and treating business in the Haynesville Shale area of northwest Louisiana. The deal hands Kinder a share of income from approximately 170 miles of pipeline currently in service, which the MLP expects to more than double to 375 miles by the end of 2010.

Together with trading capacity in the amine plants–some of which are leased from Kinder’s treating operations–this will comprise the largest midstream gathering business in the Haynesville shale. And there’s substantial capacity for further growth as well, given Petrohawk’s 368,000 net acres in the play with 4,200 drilling locations and an estimated 15 trillion cubic feet of reserve potential.

Altogether, Kinder expects a mid-teens percentage annual return on its $875 million investment, with cash flow actually ramping up over time. The MLP expects the deal to add to distributable cash flow in 2010, enhancing its ability to meet its projection of $4.40 per share for the year.

This, clearly, is the kind of deal that makes an MLP holding more valuable to us. Kinder’s new revenues will be fee-based and not pegged directly to commodity prices, just like the rest of its operation. And as management increases scale of the MLP, it increases the entity’s ability to grow even more. That means higher distributions, which justifies a higher unit price.

And that, in turn, justifies an upward revision of our target price. Kinder Morgan Energy Partners LP is now a buy up to 70.

Ditto the $1.2 billion acquisition of midstream assets Enterprise Products Partners announced April 1. Enterprise partly financed the deal with a $422 million equity offering this week. As we noted in an April 13 Alert, the $1.2 billion deal adds valuable midstream assets in the Haynesville shale area of Louisiana and Texas that will pump up future cash flow and distributions. And Enterprise’s cost of equity capital is the lowest in its history.

Consequently, as is the case with Kinder, this deal justifies a higher buy target price for Enterprise. We’re looking for another solid distribution increase for the August payment–the boost with the May payment was the 23rd consecutive quarterly hike.

That and the certitude of further boosts going forward justify a boost in our target to 35 for Enterprise Products Partners LP.

Genesis Energy LP (NYSE: GEL) increased its distribution for the 19th consecutive quarter this week. That didn’t do much for the unit price, which remains below our buy target. Nor was it accompanied by an accretive acquisition that would justify a higher buy target. But this low-risk infrastructure MLP is nonetheless a solid buy up to 21, and the distribution boost is positive news indeed.

On the other hand, we’ve yet to see this kind of cash-flow-building development with our other Conservative Holdings. That’s certainly our expectation for Magellan Midstream Partners LP (NYSE: MMP), Sunoco Logistics Partners LP (NYSE: SXL) and Spectra Energy Partners LP (NYSE: SEP). But unit prices of all three have already risen to the point where they price in a lot of favorable developments that haven’t yet been achieved.

Spectra, in particular, has been off to the races, moving above $33 per unit versus our buy target of $27. We see a lot of possibilities for cash-flow-building growth, especially through asset drop-downs from parent Spectra Energy (NYSE: SE). And there’s nothing to suggest management won’t again boost the payout this month–as it has done all nine quarters since its late 2007 inception.

That, however, is a long way above our target. And with the MLP now yielding less than 5 percent based on its current price and distribution level, patience is called for. Because of its high quality and surety of prospects, we’re willing to keep holding. But we’re definitely not raising now either.

Turning to the Growth and Aggressive Holdings, it’s much the same story now. Energy Transfer Partners LP (NSYE: ETP) announced this week what should be a cash-flow-generating event: approval from the Federal Energy Regulatory Commission for its planned Tiger Pipeline, which will also serve the Haynesville Shale and Bossier Sands producing regions in Louisiana and East Texas.

The 175-mile, 42-inch interstate natural gas pipeline is expected to have an ultimate capacity of 2.4 billion cubic feet a day and is sold out under long-term contracts ranging from 10 to 15 years. As such, it will not only boost Energy Transfer’s cash flow but will further orient it toward fee-generating assets that are immune to commodity price swings, spurring more reliable income and therefore distribution growth. That further justifies our buy target of 48 for Energy Transfer Partners LP.

Recent addition Targa Resources Partners LP (NYSE: NGLS), meanwhile, announced a $420 million asset drop-down from its parent and general partner Targa Resources Inc. These are the very best kind of expansion for any MLP, as the parent is economically motivated to ensure the assets generate as much cash flow as possible.

Prices tend to be more than fair, as operating assets under an MLP saves taxes, and this deal appears to be no exception to that rule. These are gathering and processing assets and so are somewhat exposed to changes in commodity prices. But they’re also tied to the parent, limiting operating risk. And Targa LP expects the deal to be immediately accretive to distributable cash flow, an assertion it immediately backed up with a planned distribution increase.

With our buy target of 28 still above the MLP’s unit price, we see no reason to raise it yet. But this is another good reason to buy Targa Resources Partners LP our most recent recommendation, which still yields between 7.5 and 8 percent.

We’ve seen no such galvanizing events at our other Growth Holdings. DCP Midstream Partners LP (NYSE: DPM) is still trading right around our buy target of 33 and therefore presents reasonable value. So does propane and energy midstream focused Inergy LP (NYSE: NRGY). But in the absence of accretive developments, there’s also no reason to raise our target.

Teekay LNG Partners LP (NYSE: TGP), however, has now motored well past our buy target of 27, putting it well out of reach for the moment. We still like its business model and look for further growth ahead, in addition to further acquisitions, such as the three ships added in March.

At this point, however, the best idea is to wait and see if the sizeable distribution increase Street analysts predict for May materializes. And note that Teekay is trading at nearly three times its early 2009 low and at its highest level since summer 2008. We don’t claim to be able to read minds, and we don’t have seats on this MLP’s board. But this is the kind of situation where management will consider issuing equity, which would also give us a lower entry. Be patient.

Energy prices have a very real impact on the cash flows and unit prices of our Aggressive MLPs. So it’s no surprise that strong prices for oil and natural gas liquids have spurred gains. On the other hand, investors seem to have completely ignored the negative impact of lower natural gas prices, or the risk even heavily hedged MLPs of prices remaining depressed this year.

To be sure, some of our favorites have reported very good news. Linn Energy LLC (NSDQ: LINE) this week affirmed it was 90 percent hedged at very good prices through 2013. That’s about as clear an affirmation as you can have that management has taken advantage of the better prices out on the forward curve for natural gas and is putting the cash flow to work expanding output, particularly in the Permian Basin. The company’s ability to sell 10-year notes at a competitive price in late March to finance its output expansion is another great sign.

EV Energy Partners LP (NSDQ: EVEP) and Legacy Reserves LP (NSDQ: LGCY) have also announced moves in recent weeks to ramp up reserves and output. They, too, have taken advantage of the most favorable capital market conditions for them in two years.

Weak natural gas prices will likely keep management conservative regarding future distribution increases. But these are clearly moves that make current payouts more secure and underscore our recommendation to buy them whenever they trade below our target prices. And sooner or later they add up to dividend increases. That’s also true of Regency Energy Partners LP (NSDQ: RGNC), which continues to advance major infrastructure projects that will generate huge cash flows going forward.

Unfortunately, Navios Maritime Partners LP (NYSE: NMM) looks like a potential exception. Unlike its rivals in the dry bulk shipping arena, the MLP has been largely insulated to this point from harsh economic conditions and in fact has been able to continue expanding its line of ships.

The release of the Navios Apollon from captivity by Somali pirates was also a bullish development. That not only freed up shipping capacity but also demonstrated the company’s ability to move on a global stage–the escape involved a “special effort” from the Chinese embassy in Navios’ home country of Greece.

Not even that, however, justifies what has been a literal explosion in Navios units over the past couple months. And with talking heads on investment TV recently trumpeting Greece’s sovereign debt negotiations as a positive catalyst–Navios has no exposure to Greece’s crisis whatsoever–it’s time to reexamine just what exactly is pushing up an MLP, in which we now have a staggering profit.

Put in perspective, Navios still yields more than 8 percent. But when we bought in back in June 2009, the yield was in the mid- to upper teens. That was clearly imputing too much risk. But so is the current yield providing too little compensation for the risks in this business, which could have an effect on Navios in early 2011 when certain contracts come due if conditions don’t improve.

We’re bullish on Navios Maritime Partners LP’s future. But given the profit we’ve achieved so quickly–and in light of the fact that investors seem to be chasing yield and ignoring risk–we advise selling half your position and taking a ride on the rest.

Should Navios units fall back and/or conditions improve sufficiently, we may step up our position again. Alternatively, if the MLP posts further significant gains, we may advise cashing out entirely.