The site seems pretty slick - you've obviously spent a lot of time on this, not just thrown something together over the weekend.
Are you all affiliate-based? I usually just go to ThemeForest when I want to buy something, and while I hate their browse (why would I want to see some logo for the theme instead of a thumbnail??), it does basically work.
I think you need to focus on content marketing and building an email list, so that you have some kind of community around your site (like DesignModo does). I don't think the theme search is enough to pull in customers, especially because you'll need to rely on organic search and not PPC if the margins just aren't there.
FWIW, I own www.themepuppy.com, which was originally meant to be a gallery of commercial Drupal themes, but that's not really much of a market, so I'm not using it right now.