I don't know how you predict it... 300K seems high for Fredericksburg alone, but that's obviously way too low for the state.
If you are a city or business leader, this is really, really tricky. I think many will say that while it's a big event, the $$$ opportunity is too risky to invest too much in resources. You could put a lot toward this, and then the weather doesn't work out and you have no one. And it's just a one day event, regardless.
I think many will, at the end of the day, conclude that they have to take care of public safety, do what they can to facilitate traffic flow, and just let the chips fall where they may.