A couple of points to add, Greg.
First, many (most?) of us have a membership over at MPF, but seldom log in there. I probably have looked there maybe twice in the last two years. You need to ask yourself what you can offer that would entice us back. Further, what can you do that wouldn't hurt this forum? We are all pretty happy here, and among friends.
Second, APF and NS4 work in harmony because they look at different niches. Lots of cross-posting and duplication, but different mambership and different focus. Need to understand that.
Third, the couple hundred folks that post here are probably the bulk of the internet savvy collector market. It is a niche. There are other forums here and there that dabble around the edges. I and others will generally toss out a response or two and refer back here. Examples I have worked with include satelliteguys.us in their home theater section and AVSforums.com in the theater builder section. However, the folks there are mostly looking for cheap images and their focus is the theater, not the poster.
Finally, be aware that there is a third active forum with the MOPO mailing list. Again a different focus and a different set of players. MOPO being a mailing list is aimed at folks who just want to receive news, so it is more passive. It also tends to attract more dealers and some of the higher end collectors that can remain anonymous.
So, that's where I see the situation. Show us how we can work together and what's in it for us. Also, need to know we are not buying back into the same old...