I say close it off, implement a invitation system, limit sign-ups per month (20-30?), purge inactive accounts (1 year, like someone said above), but NO frickin' FEES. I would definately not have joined BHW if there would have been a fee.
The users are the ones contributing most of the content here anyway, not the BHW founders or admins (not saying they also contribute).
If there was a fee though, most/some of the profits should go to users who have given the most. How that would be calculated in a fair way, is another question altoghether (although I'm thinking maybe by how many thanks a topic has received). This would probably give more incentive for people to post USEFUL/INTERESTING stuff.