The entire system needs to be simplified, at least to me. See I came from another CMS (PHP-Fusion), and it was super simple to setup things like the forums. I've had issues with XOOPS lately where I wanted to hide cateogories and such from non-staff/non-moderators. The class hierarchy on my site went something like this

Webmaster - Full Access to site.

Staff - Full access to all forums EXCEPT Staff category
- Cannot modify/delete others posts, can't delete own posts
-Can activate/deactivate/delete users
-Backup database
-Restore database
-Post/Modify News

Moderators - Full access to almost all forums
- Staff forums are hidden from this group's view
- In moderator forums they don't have modify/delete
other posts. Can mod their own posts though.
- Activate/Deactivate users

While this may be possible in Xoops, it's a pain in the butt to do. Currently I have everything setup the way it should be...but the moderator forums remain hidden from the moderator groups. An accidental deletion of the moderator group made it so the new moderator group I created doesn't show up as being a moderator in the forum information (at the bottom of the forums where it lists users and whatnot). PHP-Fusion accomplished this much more simply (by simply dicating who had access to what, those without access couldn't see the forums. Those without postability and access could see, but not post). You could assign it with drop-down boxes, etc. You could delegate modules to certain users via "Site Links" which allows you to administrate all of the navigation links. Some of these ideas should be taken into consideration...there really shouldn't be a learning curve on any CMS (as the entire point was to make one's life simpler). Fusion took me 5 minutes to learn and master. It's been over a week and I still feel like a noob when I'm using Xoops.

blocksadmin module is a great way to manage permissions for groups in one place. Many developers also utilize the myblocksadmin code in their modules.

But, I agree, there can be a lot of granularity in permission management, and inheriting permissions would be a great feature of any module. I've had forums that aren't viewable by a group because I forgot to set the appropriate permissions, but the category had the permissions I wanted - the forum should have inherited those permissions, at least.