Like others have said, it's easy to see the vendors and displays in a day. What I didn't count on was seminar attendance. They were quite good, and very interesting, at least to me.
At my first rally, I arrived on a Wednesday evening, but left on Saturday morning because I was meeting my wife for a concert. I left satisfied that I had accomplished pretty much everything that I wanted to. I also camped on the grounds, which worked out very well.
I met some new friends, I met some people in 3D that I'd only met online, it was a wonderful social experience.