I was considering making one of the many horrible skeleton puns, but decided against it. Rib-ticklers will have to wait, it seems.

Skeletons are mindless undead fodder, as we all know. In most cases, they're bad as PCs because they take away most special abilities then worsen the resulting chassis by giving it undead HD.

However, on a creature with one or less RHD to begin with, they're kind of interesting. In such a situation, the sole RHD gets to be swapped for a class level, and the abilities gotten arguably outweight a necropolitian's. DR 5/bludgeoning and immunity to cold, not to mention natural armor, free Improved Initiative and claw attacks are probably better than a small bonus on saving throws against undead-controlling effects.

Sure, it requires getting your intelligence back somehow, but a casting of Awaken Undead can be purchased with 3rd-level WBL, and many other templates that can also do so exist (though to be fair, most don't work on undead).

In the end, I think that in the niche case described above, skeleton is strong enough to warrant +1 LA. If the base creature ends up having to take RHD, though, +0 or -0 is probably better.