The basic wraith from the Monster Vault is light-years better than the MM1 wraith.
If the wraith gets hit by a non-force/radiant attack, it turns invisible and teleports. It stays invisible until the end of the encounter or until it attacks, but it cannot attack until the end of its next turn. Combined with the fact that, as Neonchameleon noted, it does much more damage when it is invisible to its target, and this guy really plays like a lurker.
I probably wouldn't run more than one or two (having lots of invisible teleporting foes that can't attack might get a bit frustrating for both the players and DM), but if combined with some more conventional foes, the DM can really have fun.
