It seems to me that most of the administrative functions in OpenACS are sound, and that most of the admin usability problems are labelling and organization. I see only two fundamental issues that may need serious code to fix:
1) the sitewide/per-site split
2) the bewildering terminology for user groups (Group Type, Relational Segment, Relational Type, Composition Relation, Membership Relation - a set of words that could arguably be hidden/simplified in presentation until only "group" remained)
For everything else, there's re-arranging. Here's my first stab at identifying commonalities between the admin functions:
https://openacs.org/doc/openacs-HEAD/images/adminia.png