I think the category permissions should be split out from the category options page and into a separate usergroups-based permission just like resource categories do. Would make things more consistent.
I am also voting for this consistency improvement. This is really needed.
Right now, I am not able to set usergroup based permissions for categories which makes me rely on user's faith not messing up things.
There should really be node permissions like any other addon has.
We cant even hide a category from guests. @denam please add your vote to the first post if you want this implemented.
You can hide a Media Gallery category from guests. I have a category and several child categories that are visible only you Registered users. You simply edit the category in the ACP and for "Usergroups that can view this category and its media" select the appropriate ones (in this case, Registered". Repeat for any child categories.