Yes, all three of the trails I mentioned are public access. However they are not without issue themselves though. They only remain open with effort. Maybe Russ can chime in on that. I'm pretty sure VTXS has been involved.
-Yep, MaBell is open to the public. It gets heavy, heavy use though and some days if you get there too late you could be waiting in a long line of (mostly) Jeeps hammering through the trail.
-I believe that ArmyRover mentioned that he didn't see EC4WDA doing a group thing to Winter Romp. That's because Romp is primarily a Land Rover Event.
-Perhaps you should look more into NE4WDA instead. The largest benefit to a group like this is access to private land. These guys typically have permission and organized rides on private land that can blow your mind by how good it is. Yes, there is a fee for these groups but it can be worth it if you take advantage of what they offer.
-If y'all are looking for something to do I highly recommend putting the effort in and doing something big. I just did 2 days at Rausch Creek in PA with VTXS. We rolled in Friday night and set up camp right there and spent Sat. & Sun. wheeling some incredible trails and we barely covered a fraction of the available trails. (link to photos:
http://picasaweb.google.com/russ.bowles/RaushCreekApr08?authkey=gXhF_bWU7Qw ) If you have the time to spend doing something like this I highly advise giving it a whirl.