Thinking of what A1GP needs for their paddock, which tracks would be a good fit (just talking facilities). Factor out Indianapolis as it's obvious that track does due to the upgrades for F1.
Miller Motorsports Park was very popular with World Super Bike, but I would prefer Laguna Seca. They have been there once (the weather ruined the event), but we need open wheel cars in the corkscrew bad.
Virtually no rod racing track in the US has the facilities for A1GP because they arrive with all their equipment in air freight containers and the cars on pallets. The tracks they run on therefor have to have Indy or Montreal style garages. Watkins Glen might work in a pinch but Upstate NY is not suitable for a winter racing series!!
Miller and Road America both instantly come to mind, but how about the new track in New Jersey, it might be tough in the winter but it shouldn't be that bad