So many mysteries to solve, so little time. Despite a growing chorus of skeptics, Icahn Enterprises (NYSE: IEP) just keeps chugging higher, leaving its net asset value far behind. Carl Icahn’s partnership is now up 55 percent since we recommended it two months ago and 15 percent since we advised selling half of your initial position three weeks ago.

Carl Icahn is a real mensch and a great financier to be sure, and his aggressive shareholder activism and loud proclamations of value have made him the Pied Piper of this bull market. Still, there’s that net asset value disconnect. And the reason it has opened up, and could well persist, is that net asset value doesn’t pay distributions.

There is a real shortage of income out among us, be it the income missing from the jobs permanently gone or from the low bond yields that have upset so many retirees’ assumptions about sustainable withdrawals.

Relatively high-yielding vehicles like MLPs and mortgage REITs have filled this void, and this more so than their tax advantages may explain why MLPs enjoy such a valuation premium over their C-corp income-tax-paying counterparts.

Berry Petroleum (NYSE: BRY) was paying a dividend yield of less than 1 percent before Linn Energy (NYSE: LINE) came along with a premium takeover bid that will now harness Berry’s assets to support Linn’s 10 percent yield. And why was Linn able to pay such a premium valuation? Because its equity was already richly valued based on the 8 percent yield it was paying at the time. Linn’s trying to prove that’s a virtuous circle.

Icahn surely understands the advantages of a nice yield as well. The small sliver of his partnership he doesn’t own was floundering below its net asset value last year, when it paid out a measly 91 cents per unit. Then — boom! — the 91 cents per year became a buck per quarter early this year (later raised to the current $1.25), and we now have the results before us.

The increased distribution is what allowed me to tease September’s pick with the promise of a 6.6 percent yield. Those were the days. It’s 4.3 percent now.  It’s telling that in cautioning investors about IEP’s alleged overvaluation recently, Barron’s pointed to the net asset value discount that still pertains for another investment conglomerate, Loews (NYSE: L). Well, Loews distribution currently yields 0.5 percent and has been flat since 2006. Interested yet? Allow me to suggest the yield disparity might have something to do with the valuation disparity.

Here’s where the net-asset-value analysis goes wrong. You can buy shares in Federal-Mogul (Nasdaq: FDML), the auto parts supplier majority-owned by Icahn Enterprises, directly for less than IEP’s price implies, but they don’t pay a regular dividend. Same with Tropicana Entertainment (OTC: TPCA). Icahn’s subsidiary energy and railcar interests do pay dividends directly, but the only way to participate in the profits he’s earned by setting off the Netflix (Nasdaq: NFLX) bull stampede is, again, via IEP. The partnership’s income is highly cyclical, but for the moment the cycle is still turning in the right direction.

Source: partnership presentation

And yet Icahn’s profit flow is, at the moment at least, considerably richer that most energy MLPs can muster. His latest report showed three times as much income as needed to maintain that 4.3 percent yielding distribution. Elsewhere in MLP land, distribution coverage only half as good is cause for celebration.

So yes, regular income fetches a nice premium these days. Kevin Kaiser, the Hedgeye analyst bearish on MLPS, points out that the more expensive ones match Google’s (Nasdaq: GOOG) valuation on a cash flow basis. Google, of course, is still growing by some 20 percent annually, a rate only a few MLPs can hope to match. But it pays no dividend. And, given the alternative of a steady-paying MLP, investors don’t appear all that interested in in harvesting future income from Google’s as yet unrealized capital gains.

To point out a valuation disparity is not, of course, to suggest that it will go away soon, in fact my point here is that it may not. But the disparity exists nevertheless, and may limit future returns if the psychology turns. A 3.5 percent 10-year Treasury yield is likely no long-term threat to the valuation premium MLPs. But something closer to the long-term historical average of 6 percent certainly would be.

And we must remain vigilant even in these low-yield times to the possibility that a high yield can’t be the only investment criterion. For instance, we’re dropping Loews subsidiary MLP Boardwalk Partners (NYSE: BWP) from the Conservative Portfolio this month, because despite its heady 7.6 percent yield it’s no longer either a conservative or an attractive investment. Boardwalk’s core business of transporting Gulf Coast natural gas north is in decline as a result of competition with cheap Marcellus gas, and an unsustainable yield is no consolation.

Recent portfolio addition MarkWest Energy (NYSE: MWE) also disappointed with subpar earnings, but its medium-term future still looks bright. And other recent recommendations, notably Energy Transfer Equity (NYSE: ETE) and EQT Midstream (NYSE: EQM) have continued to power higher despite modest current yields. Investors realize their distributions are headed significantly higher in the years ahead, barring the unforeseen. We have earnings news for the vast majority of portfolio picks in Portfolio Update.

Concern about the state and direction of the underlying business rather than the nominal yield also informs this month’s Best Buys. Dry bulk shipper Navios Maritime Partners (NYSE: NMM) offers a double digit yield on a distribution that’s likely to hold steady throughout 2014, with decent odds of rising thereafter given the shipping industry’s improving fundamentals.  Targa Resources (NYSE: TRGP), the sponsor and general partner of current Growth Portfolio holding Targa Resource Partners (NYSE: NGLS) offers a much humbler 3.2 percent yield, but promises to hike the distribution at least 25 percent next year, after 30 percent growth in 2013, thanks to its strategic position in processing and exporting the flood of natural gas liquids on the Texas coast, a stream that’s sure to grow significantly in the years ahead as well. These are the businesses we want to own for the long haul, not for their next distribution.

In Focus this month is the nasty fight at the Federal Energy Regulatory Commission (FERC) over the fees Conservative Portfolio mainstay Enterprise Products Partners (NYSE: EPD) and its Canadian partner Enbridge (NYSE: ENB) have been charging to customers of their jointly owned Seaway Pipeline. The full commission is unlikely to follow the advice of its own staff and an administrative law judge in cutting committed shipping tariffs on the pipeline by up to 84 percent, and if it did this cut probably wouldn’t hold up in court, in my opinion. But the contention that the Seaway could earn a fair rate of return by charging a small fraction of the going rate does illustrate the recent gains of crude oil shippers.

Finally, this month’s Sector Spotlight details current  midstream assets and new ones proposed for the Permian, one of the oldest US basins but also a fast growing one thanks to advanced new production techniques. As long as drillers continue to extract an ever growing bounty from domestic wells, midstream investment will be needed to ship, process and market the hydrocarbons. And so long as that’s the case, you can safely ignore claims that MLPs are in a bubble. They’re simply offering something particularly scarce at the moment: regular, predictable investment income.