I think my answer is going to be to sort-of-overload the group and topic 
levels, which I was doing pre-REST.

Right now, if you look at
http://forum.phoenyx.net/group/
you'll see (with a webforum template) *all* the topics, including their 
last-post and post-count information. Pretty much a standard top-level 
webforum page.

I think it's still RESTful... it's the representation of a "meta-group."