I guess the market will decide what a fair price for any project will be? If the site works like I think it does (could not access it, server down?) I can imaging buying a project, working on it for a few months and then putting it back up for sale to maybe make a little profit and see some one else bring it to completing.
The market deciding only would work right when there is perfect information. I'm not sure about that.
Take the twitter valuation, and say to yourself "well even if I'm only 0.1% as successful as twitter is...." and go from there.