That's a good suggestion. In some meetings, like the monthly roundtable meetings, we've been talking about hiding (with categories and permissions) old wiki pages that aren't useful anymore. Probably the same thing should be done about forum posts, if they don't have any value even as "historical documents", etc.
I agree about searches. It seems to be a powerful feature but the filters don't seem to be working right, in my attempts anyway. I think this is a known issue so hopefully it will be improved.