Is there a reason to run the specialty races at Indy other then its Indy? If it's like the Big Bud then you have to "qualify" to run at the specialty event, right? This would mean that only top 10 cars, or top 8 cars make the special show, and its guaranteed that those top 8 cars travel the full tour - therefore there's no reason to hold it at Indy due to its centralized location.
Makes sense to hold the specialty events at two tracks that are both state of the art and have the best attendance. I don't know what the best attended races are, or the state of the art tracks, but I'd think the 3 options would be Vegas, Norwalk, and Charlotte. That's a pretty good spread through the country too, so nearly everyone has a chance to go see one (if theres a special race for all 3 classes) - Of course, for those of us in the north central part of the country (MN) we don't get to see a specialty race unless we're flying and putting out the money. (We do get snow mobile racing though--- ugh)