LJ45,
All of the organizations have their useful purposes. NBAA is one out of those that you named that is going to be focused on Business Aviation more so than the others, which might encompass several aspects of aviation, such as the AirCarriers or Bonanza pilots for example. NBAA will fight fights that they will never win. DCA is a good example of that. NBAA needs to focus more on what they can do instead of wasting time on pipe dreams, but I would not walk away from them. They do have lots to offer.
Look back a week or so and there was a Hawker pilot on here explaining how to join NBAA and listing some of the resources and services they provide and he was correct, it is an excellent tool when operating in a corporate aviation environment.
As was also the case, there will always be someone that is going turn their nose up at a group like NBAA. Although I found it odd to see someone on this forum doing that, I was by no means surprised. There will always be those who do that, but I would encourage you to find out for yourself what all of these groups have to offer and pay no attention to those who think they know more than they actually do.