I think this is a really great idea.
I do, however, think that either a wiki or forum could work, but I fear it might "overload" or otherwise "mess up" the wiki/forum we have. What about installing another, separate wiki or forum installation dedicated to this? They already allow both file attachments and edits/updates.
Actually, the first thing I thought of was a revision control system (e.g. CVS, SVN, etc.). This would prevent the problems of "complete new archives just for small changes" and "the scattering of small changes over numerous posts" (see: the forum posts about "crt0.s" and "makefiles" for examples of the latter...

) while also providing a convenient backup/restore system for contributors. The main problem would be no way for members to easily comment on projects/assets (do any existing R.C. systems have this functionality?) other than "readme" files. (Based solely on
this old blog entry, I suggest "Mercurial".)
Another, albeit less powerful, alternative would be a simple FTP site. To make it a little more "high-tech," there could be a 'bot that generates thumbnails of images found in new/changed submissions.