Recently I had a client who wanted to use MoinMoin as a simple CMS. He requested a CMS-like theme that hides the edit bar and actions for anonymous users. He also wanted to hide all (most) system pages for anonymous users, as most of MoinMoin's help is only useful for editors anyways.
One way to achieve that is to set acl_rights_after to "All:", and then acl_rights_default to "All:read", or add appropriate acls to the "publicly visible" pages. Unfortunately that won't work, because many (but not all) underlay pages have an explicit "All:read" acl included.
Another way would be to have some sort of acl_rights_before_underlay that would only apply to system pages.
In the end I just told the client to set appropriate ACLs in the underlay directory with sed, and repeat it after every upgrade.
moin 1.7 will have different acl lines on the underlay pages. Basically they are just "-All:write Default" - taking away write rights, but using your acl defaults for everything else.