What if you could change your wall so that only your friends and mods could post on it? It would cut down on the spam because the spammers would have less areas to spam making it easier to catch them.
even if you created a forum for only your friends there would be 1. too many people asking to be your friend 2. if you have few friends then a conversation wouldn't carry on very well 3. You can still carry on a conversation with a friend using The Messanger