Last year I went to my first Friday evening event, and like you I was concerned about seating, so I turned up early. However the seating wasn't bad at all to get, and I wound up walking out to grab a quick bite to eat before the main events started.
For my money, I think the best spot to watch is on the second curve, by the steeple chase water pit. You are super close to the action, and not a lot of people gathered there. And then you're in a perfect position to hi five the athletes when they do a victory lap. I plan on standing there this time around too to watch Mo race.