Looking at Gate 10's website, it notes that the online listing for GenCon is all closed and done, but implies that there is still parking available on a first come, first served basis.
Does someone getting into Indy in the early afternoon on Wednesday have a sporting chance at getting a spot, or is that just a pipe dream? If they will let you in, will they let you get a spot for the weekend, or are you on a day by day basis?