The bigger problem is that not only will htere not be enough hotel rooms - but all of the rooms available will at least double in price. Trust me on this, here in Birmingham (about an hour from Talledega) the hotels book up completely - and those rates go way, WAY up. (2X or 2X) and they require you to book at least three nights.
So if you keep GenCon on that weekend - you lose a lot of people due to the fact that they can't get rooms, more because they can't afford rooms (NASCAR could quite possibly fill every room by itself), and those that do make it will have a LOT less cash to spend even if they do make it.
NASCAR is huge and it overwhelms everything -restuarants, hotels, .... just everything.
Having GenCon during the school year might be bad - but it pales in comparison to the disaster that could be NASCAR. (Consider that the only kids who would be affected would be local school kids - because I doubt that out-of-town youngsters are going to be able to afford NASCAR-weekend prices on lodging, anyway)