It feels like a ghost genocide instead ghost hunting xD.
Also, how about different weapon pickups (with limited ammo)? To make killing stuffs even crazier on those big number of ghosts :D.
Played your update. Nice start for improving your game after game jam ;).
Some thought again when played the game:
Also a question, why not making the wave attack killing instead of pushing? It would make killing crazier, but with cooldown to balance it ;).