The more members you have, the more potential customers. I'm sure that a lot of people would be interested in making that kind of money from the web, especially when the members make most of the content. People would pay extra for the content, and the members, and the Search engine rankings. There are a lot of good things going for your site, and if it is making $11,000 per year, then it is definetly worth many times more than that!
I'm sure that many people are wondering how you have made such a great site. Could you share some of your promotion advice with us? What is the URL of this forum?
I'd rather not disclose the link, I have great relationship with my community and dont want them to think I'm interested in selling it.
As far as promotion goes, I try to form relationships (biggy) with non-forum-competitive webmasters in the same genre to gain large chunks of traffic from sites without forums. SE rankings with main site pages (normal pages) are great for very general content. I keep advertising to a bare minimum and have a great (large, quality) volunteer moderation team made up of the prominent, most intelligent, able members.