Re: page permissions
Is anything holding you back from giving the group "users" the tiki_p_view and tiki_p_wiki_view_attachments permissions, in addition to the three permissions you mentioned ? I don't think it's a problem with two user groups having any of the permissions...
Your page permissions would look something like:
| Anonymous | tiki_p_view |
| Anonymous | tiki_p_wiki_view_attachments |
| users | tiki_p_view |
| users | tiki_p_wiki_view_attachments |
| users | tiki_p_edit |
| users | tiki_p_upload_picture |
| users | tiki_p_wiki_attach_files |