Doesn't the new owner have to pay a $100 free for the re-install and/or having the script licensed to him/her ?
So if boneprone would give you $600, it's $100 for the design and traffic
(
if it's not true about that $100 fee, disregard this post )
I think your site rocks, i'm sure if you update it frequently and get some nice trades going you can get it alot bigger.
just my ?0.02