I like what you said here. Contrary to what people seem to think...these "be all, end all" services and sites aren't suited to very particular and niche markets.
It's funny because there are so many people on HN and Reddit, for example, who don't capitalize on creating small niche services because there's already a Flickr, or already a Youtube and whathaveyou.
So I think you've done a good job here.
I think you could probably market $10 better. Remove the struck out $20 and just prominently and proudly display the $10.
As a risky marketing move, how about refunding all users who paid $20 the difference? What a great way to get them talking about you on Twitter, Facebook, etc. when you deposit their account with $10. It's a nice surprise.
Just an idea. Good luck.