I'll try to answer some of your questions...
The restaurants do close at whatever hour the park is closing, be it 6pm as it is now, or 7pm later in the season.
Some people do stay for the GAC Tonight show and leave at intermission, about an hour into the show.
This time of the season, traffic seems to move pretty smoothly going out of the park. It can get backed up coming into the park in the mornings. On Saturday, you might get caught in a bit of a line leaving between the hours of 3pm and park closing, but as I said, it moves pretty smoothly. It's not like you'd be sitting in one spot for even 5-10 minutes, and I would venture not even close to that long. I really don't think traffic congestion will be that much of an issue unless you're here on a high capacity day.