... that you don't get bored revisiting the same room again and again each time you start a new character?

I'm really not sure the perks you get from OXP/EXP generate more "engagement": I doubt CF numbers would go up even if you would get more perks from this tedious aspect of the game. Personnaly I think it's just boring and a waste of time. And since this game is already so much time consuming, I think getting rid of OXP/EXP has a lot more potential to bring people back than any of the other suggestion mentioned in this thread. But that's just me... maybe you (and others?) like doing the same thing over and over.