I'll do content, but I really don't want to try to customize a Wiki. TWiki is already geared more toward logged-in users than a traditional Wiki. I think there's already an option to require confirmation of new users. Let me check the docs a bit.
Also, we should probably look at doing an upgrade. There's been quite a few security and functionality updates since ours was installed. I know you've been on top of the patches, but it doesn't have that "new installation" smell any more.