Mortals who become spectres are turned into incorporeal mockeries of their former selves, without compassion, mercy, or nipples (as shown by the above picture).
They have 7 undead RHD, and the ability scores they have all get boosted. Their flight is 80 ft. (perfect), which is nice, though I'm not sure why they have a land speed. They get a small amount of turn resistance, and their natural attack is a 1d8 damage-touch that also inflicts two negative levels. In true incorporeal undead fashion, the ones they kill turn into more spectres in a few rounds, which are obviously enslaved by the original one. As with all unlimited spawn-creation, I won't be considering it when assigning a LA.
Two of the spectre's other abilities are Sunlight Powerlessness, which removes your ability to attack and eats your actions if you're in true sunlight (ouch), and Unnatural Aura, which will scare your druid's companion and protect you from annoying wilderness encounters but is otherwise not that important.
I couldn't help but be reminded of the shadow as I wrote this. In terms of HD the spectre is in between regular and greater shadows, but it has better stats than either, what's probably a slightly better damaging mechanism, a higher speed, and stronger spawn. At least +1, and possibly +2, seems reasonable here.
I'll go with +1* for now, but please share your opinions.