I talked with Dave about this about a week ago. I agree strongly with both of you.
What's most missing from the OpenACS main page is WHY THE HECK WOULD I WANT TO USE OPENACS? (sorry for the caps)
I've written up some preliminary stuff on this at:
http://rubick.com:8002/openacs/book/why_openacs
(registration required)
Dave said I could put up a preliminary "Why OpenACS" page and we could link to it prominently. I think that's a good idea (and others could edit that as they like). But I agree with Chris and Joel that the front page could be substantially improved.