Good points here -- I'd like to see the capabilities added that you've identified.
You bring up some great points, and improving Tag Groups (aka Tag Folders) is on our radar. For the 3.5 release we're going to be maturing Tag Groups somewhat, but we won't be able to address this specific request due to time constraints until a future release. This enhancement is filed as CS-8298.
About them not showing up when customizing Group overview pages, we are planning to add that to the set of Group and Project widgets in the 3.5 release.
In the future, a great place for product-specific feature discussion is in the Jivespace Feature Discussion.