I would say if you get the forum more active you could be doing well. I would say put them in rotation but only a couple a month at 100USD a piece or what ever you think is right. Also if you have a network of sites its best it goes smoother to tell people you will be putting their banner on your network of sites for more exposer
i used to own both unreal-2003.net and unreal-2004.net - we were a pretty succesfull gaming community but i had to pull the plug on it which was a shame