Alright. It looks like the Clean Install did the trick. Of course I'm back at square one as far a customization goes. I've decided not to try and use any of my old profiles, I've created a new profile and I'm setting things up from scratch then I'll export a backup. I also, immediately, made a copy of the OOTB <<Civil 3D>> Workspace, so that should be intact if I have to revert to it.
I'm a little disappointed that this is the second clean install that I've had to do in the past 7 or 8 business days. But if it works for a while now I'll have to be happy.