Admittedly, I think if fanart was banned from the AA, I would buy less from there. It's not that I don't like Original stuff, it's just that I have no real connection to someone else's OC. I don't know the story, and just because it's original doesn't make it good. Just like in the dealer's room, people (ESPECIALLY those with a limited amount of spending money) are going to buy the things that are familiar to them. It's as simple as that.
And I understand the reason to ask lawyers, but really, wouldn't asking the companies be better?
If derative works are protected, and the only reason fanart can't fully qualify is because permission needs to be granted....why not just ask permission?