I would be curious about what others have to say about this b/c we recently started www.indigames.org which is similar to your site in that its a forum. You appear to have great membership. What is your average monthly reve? My opinion about the value of the site might change depending on ad income.
As you know forums usually have low CTR so I display adsense to guests only. We have banner rotator setup instead + premium/vip membership I actually want to know the domain value, we are on the google's first page for keyworg "gfx" and recently we recieve a lot of traffic