After thinking it over, I think PoW does make sense if it's recognized at the account level, so that way it is reusable. If that trust is abused, the account can be blacklisted. That makes more sense to me than requiring PoW at the event level, where it is not reusable.
Discussion
As in relays will check account level PoW for spam prevention or accounts in the client will set what they expect from accounts they follow among their relays? Or both?
#[6] was talking about PoW being required until account level reputation is achieved, so this kinda goes well with that. I like it.