Re: Kill all the Wraith-men...
The spell only works on critters Susceptible to "holy-ocity". I can't find wraiths in HS Beastiary. Where'd you get them?
Remember, Susceptibility only does STUN. No BODY. If the PC can take out a critter by adding 1 or 2 or 3 dice of STUN, with almost-one hit, he probably doesn't need the blessing, much.
If you goofed and did 1 or 2 or 3 dice of Killing Damage, that would mean he needed the blessing. It also means you got to go back to the players and say "Ooops! OK, now on, that blessing only does the damage it was supposed to. Sorry for getting it wrong." If your players are good folx, they'll understand. If they whine/throw fits/complain, they're bad players and no friends.