Hi Mark, thanks for giving this background on the forum. It was good catching up with you by phone yesterday, too, to hear more detail about the choices. To reiterate that for the benefit of the broader community, I think that the key issues you're raising here have been experienced by many and it would be good to hear from others about how they have addressed them. These are, as I see them, as follows:
1) How do we leverage our current success at promoting collaboration to the next level?
2) How do we select the right sorts of collaboration platform that fits the business need now and will scale for the future?
3) How do I select from the myriad platform options that are out there?
Let me suggest that the beginning of this conversation is a review of the elements of collaboration that have worked for you so far. It will involve looking at the pilot groups and not only what worked for them (in your case, the Google Groups email list) but also what didn't (Moodle) and hypothesize some reasons this may be because of the specific audiences you were trying to help.
If you think about your collaboration goals, you need to start planning platform features based upon the collaboration activities that will best serve your target audiences, your key messages that you will use to help drive adoption of the new platform (show what's in it for them to make the change), and the business outcomes you're trying to drive, as well as how those outcomes will be measured on on ongoing basis. If you don't take this user- and business-centric approach you're sure to feel overwhelmed by the many pro's that each platform vendor will try to sell you on.
I hope that this helps. What have others on the community in a similar situation done?