Well, thats interesting Krazie, wraiths are expensive, and do HORRIBLE ground damage, and have little life.

3 observers make them almost useless, in any attack with protoss.

Overlords, make them almost useless, again.

Only effective, imo, against un-obbed carriers, or with other units (microed effectively) in a TvT attack.
Wraiths depend Heavily on other units (sci vessel, valk, bc) and other air units depend on them (again, sci vessel, valk, bc)