Just a thought, but why not give a little credit to the paying people..
Not litterally of course but like if you contribute (financially) you lose the ads..
This might give more paying members.. ads and banners are an annoyance. If you lose the ads and banners with a donation of $5,- or higher this might help in getting some money in...
Just an example of course..
I didn't think of this, there are other communities that work like this.
It's always free but you get a little extra functionality to make life easier if you donate..
Very reasonable I think and members get something back for their donation.