I participate in quite a few other boards that use UBB software. While I think the advanced features they offer can be intriguing, I don't think they're appropriate for Flyertalk. In short, there's very little gained considering the massive downside potential.
I understand why others might want them but considering that we have issues with inappropriate signatures as it is, I think avatars would simply be ripe for abuse and would distract from the main thrust of points and miles. Another consideration is that as we are much more a global board than others, an avatar considered appropriate in the US or UK might be horribly offensive in Asia or the middle east and so on and so forth.
As for reputation, that was an unmitigated disaster. Thankfully that feature rolled out before I was a moderator! I've never seen more adults throw playground-style tantrums over a ding to their reputation than during that period. It needed to be turned off. Far too many people used it for personal entertainment purposes as opposed to the poster rating system it was supposed to be.
What might work is a thanks system whereby FTers can click on a helpful post and 'thank' that person. While still subject to people gaming the system, it wouldn't be open to the abuses the reputation system is.
Beyond that, I like the simple style of FlyerTalk, especially when abroad on a slow connection. I don't want bells and whistles; I want easy access to my points and miles info! That, FT provides as it is in spades.