Did you ever get an answer to this question? There's an add-on for the Firefox browser that's supposed to parse JSON files but it gives an error when opening the Ning archive files (can't parse because the file is not "well formed"), so I'm thinking maybe it's the same problem you had. Have you found a way to deal with this? I tried editing the files and removing the "(" but of course I can't save it as a .json from the editor. Any ideas?
Any thoughts you have will be appreciated.
Sorry for the late response. You can email me at caveatrob at gmail dot com if you want to discuss further. I've written a JSON parser for members and blog posts. It's pretty crude, but I could probably work out a simple CSV export for you if you like. Ping me late next week when my semester will be over.