Is it at all possible to allow users to create & post to public albums (and categories) which other users can also post to without giving users full-blown admin access?
It's possible to allow users to upload to public albums (groups page (http://coppermine-gallery.net/demo/cpg13x/docs/index.htm#group_cp) and individual album's properties (http://coppermine-gallery.net/demo/cpg13x/docs/index.htm#album_prop)). However, it's not possible to allow them to create albums in public galleries.