If sneaking for the sneak attack is that important, then the stat bonus of the elf in Dex gives bonuses to hide and move silently. I'd say that makes up for the hit to con, especially since with a point buy system you can get a 12 con (after adjustment) pretty cheaply, which is enough for a sneak build (majority of points would go in dex and int, natch).
Note that if one is useing lowlight vision to flank in that area of light that is shadowy to the victim but not to the half-elf, wouldn't the victim move, either fully into the light or fully away from the light? Or do we require stationary victims too for the half-elf to shine?
If you are thinking of sticking around in meelee more, then you should be thinking of a fighter type anyhow. And now dwarf and half-orc start crowding the scene.
Also, this lowlight vision is less useful in dungeons, temples, other indoors stuff than darkvision (where 60' is plenty, except for corner cases of freaking huge rooms). So the half-elf is the outdoors kid or the townee kid. Again, the elf does better at the spot/listen side AND the hide/move silently side.
Heck, if darkvison and movement are that important, now the goblin looks great, but of the core seven, you might even take the int hit and look at the half-orc.
The half-elf has nothing to *be* and nothing to *do* that other races can't do better. While no single race is better than the half-elf at each particular thing, there is nothing that the half-elf is better at (except such a small amount of corner cases that you pretty much have to hope that your DM tailors his campaign to favour half-elves - (lots of low-light chances (lots of starry lit cloudless nights, no underground activity, little daylight activity), high diplomacy (night time interactions), high gather information, perhaps odd prestige class (where prerequisites require elf blood and strange mixes of non-wizard classes - fighter/sorceror/arcane archers and the like?), AND as high a con as possible (so frequent combats on these starlit cloudless nights above ground, relatively few combats elsewhere or when)). I have never been in the latter campaign, and from the looks of the posters on this thread and the half-elf thread, it looks like few of the posters have been in such a campaign.
