I think that the CodePlex, Google Code, GitHub, etc. for source code/project management is a good idea. They also have issue/bug trackers which will make handling things a bit easier to track.
I'm not an expert on WPF (nor WCF, but I've used WCF more frequently). Over the last several years, I've kind of went in the web forms (asp.net) and class libraries route. I used to do a bunch of win forms, but not so much anymore. Comicster's selling point to me was the plug-in model approach. It's much easier for me to crank out plug-ins for things I want to do or modify existing apps, then to write my own from scratch - which I had started on, but due to time constraints it would have taken me too long to finish.
I'd contribute some of my free time to help getting the base version up and running (testing, coding, or whatnot). I think it would be a good idea to spec out what the current version has (features-wise) and then try to finish getting the next version to the same feature-level (along with some of the extras like the ComicVine API, etc.). I'm a big believer in that newer versions (even re-writes like this) need to start off in at least the same feature-set as the previous version. After the new the version is stable, then I'd like to test out writing a few plug-ins for things that the app might need on top of the base set of features.
I'm looking forward to seeing comicster moving forward :)