I have been playing the game for a while and I have collected a few of these, but I havnt noticed them providing any in game rewards or anything. What do the dead ghosts do? Is there any point in even collecting them? I would assume there is a bonus of some kind for collecting them all or something, otherwise they would be a pointless addition to the game.
As far as I am aware, there is no in game bonus for collecting them. They are just a collectable item that some.people find fun to hunt for. There is a trophy/achievement associated with collecting them if you are into hunting for those.