Hello
Firstly, your site didn't even load for me so that's not a good start! Secondly, the traffic isn't that great really....have you been advertising it? And finally "potential" revenue isn't what sells sites, if your site isn't making anything then it's worthless.
I can't see the site to view the design but at the moment i'd probably value it at whatever the design is worth/domain/traffic....I'd say around $300-500. I do like the concept though! Would be good if you could have a feature to password protect the psd files....might make transfering clients work over alot easier