I think that it would be totally cool for this to be your new project. I start things all the time and never finish them and to be able see my ideas(which I think are brilliant, then again I'm biased :) ) come to fruition would be awesome.
That being said, I have at least one project I wouldn't mind donating. If you know C#, let me know and I'll send it your way (if you want it!)
Liam there is a market for selling an incomplete technology but someone picking it up to complete it. Many business buy other businesses. I don't know though of an easy way to look this up and find potential businesses that have run out of funding but have an idea that you could buy and make your own. Perhaps that's a new service to be offered? Hmmm
There are plenty of projects on google code, github, and more that have not had attention for a while. If you are looking to do a commercial project, it may be best to start from scratch on your own code. Of course you can take a look at what is out there for inspiration and ideas.
In my experience there's nothing worse than working on another software engineers code, I always say do your best to ensure the original coder stays on the project. In that sense, the money in software is about paying the right developers to carry on coding, not taking over projects.