Hmm if you haven't had much previous experience with code collaboration then opening up your.flowingdata to too much development might be overwhelming. You could consider making the code available through something like github.com (if you have the code under version control using Git) where people can fork the code, make patches, and submit the patches for you to review.
If there are specific features you are interested in having people develop, it might be good to think about creating a list for people to work on. The Dreamwidth community has done a really good job of making it easy for people to contribute in a directed way (http://wiki.dwscoalition.org/notes/Development), but it's also taken a lot of work to set that up.
In any case, I'd be interested in seeing if there are ways I could help out.