When do the gates open for spectators?

I also think it depends on the event. Whatever the event...find alternative parking if it has rained or will rain when you are there. You take a good chance on having to get pulled out by a tow truck ($100 at the balloon festival) like a friend of mine. That will surely ruin your day.

I would say it depends on the event

I believe when we went it was 9 am during the balloon festival they open at 5 am for the morning flight. Not sure about the rest of the festivals held there.