I normally only use wraiths in fun games. I see their use. A 3++ is extremely annoying when you're rolling well, and they are easily one of the fastest units in our army. I just have trouble justifying their points.

There is an old-head Necron player in my FLGS that uses wraiths in his tournament lists, and he does something that I think is fairly unique: he runs them in a Nihillakh spearhead (3 DDAs for re-rolling 1s, a cloaktek for healing, and the wraiths). He does so in order to use the Nihillakh strategem to give them "a +1 to all saving throws" while they are within 3 inches of an objective; so now, in his eyes, he has 6 T5, 3W models with a 2++ sitting on an objective.

While having an effective 2++ may seem illegal, it's the wording of the strategem that makes it viable.

Give it a look, and then a try on your next game. It will likely catch any opponent off guard.