I have been to a few and they are pretty interesting, This year the rally is selling day passes as well. Usually some decent seminars , interesting vendors and other stuff.
Camping on the fairgrounds is the way to go.
You don't have to own or ride a BMW to attend.
The riding schools fill up fast and the MOA offers shipping to send stuff home.
I have scored some decent deals on stuff in the past at rallies. Good tire prices and they install them while you wait.