LLLL.com domains should be evaluated, individually, based on traffic, current uses of the acronym, the popularity of the acronym, and potential demand for the domain (partially indicated by other registered extensions and how they are being used).
I think the "bottom-of-the-barrel" or "low-demand" LLLL.coms are those with no other extensions registered, they get little or no type-in traffic, and there are very few uses of the acronym (few Google matches) and the matches that you find have little relevance to anyone. Even these (less-popular) domains have value, simply based on their length, the growing demand for short domains, the growing number of investors, the potential for any LLLL to assume new meanings in the future, and the potential, unknown, new uses for short domains in the next few years.
Some people talk about how LLLL.coms aren't worth much because there are so many combinations and a lot will go through drop cycles. There are 456,976 possible LLLL.coms, but considering that there are now over *100 Million registered (or "Active") domains (.com, .net., .org, .info, .biz, .us), LLLL.coms make up less than one-half of one percent.
The current value for (low-demand) LLLL.com names is between $30 to $50, and I predict that $100 will be a minimum (speculator) price for these names within a year or two. Of course, prices will vary depending on the perceived value of the domain by both the buyer and seller.
In my opinion, the current end-user price for any LLLL.com domain should start at $1,000, and the price/value should be adjusted up, based on traffic and PPC revenue, and any other indicators of current or predictable use of the acronym.
* STATS:
http://www.domaintools.com/internet-statistics/