Keep at it guys you can make a differance. We had a local oval track basiclly legislated out of business...the owner had to make many improvements and then when he had to pave the dirt parking lot it was more than the place could bear.....the best part is the empty parking lot is a place where folks started flying RC airplanes and making more noise then the track did.
Matt as far as Riverside went , the land just became to valuable. I raced the my bike there before the end and it had become a hole , it needed to go. Track was very bumpy and management was milking the place for the last 5-10 years.
As for places that don't have this dilema; California Speedway is on the old Kaiser Steel yards so due to HAZMAT issues it can't be used for anything other than a racetrack. Las Vegas Motor Speedway is in the crash zone for Nellis Air Force base so it too has very little use beyond a track.
Our local club course is located in a small community that welcomes the revenue brought in by the extra 50 or so hotel rooms rented out every weekend.
Lesson here , there is land that has no use and communities that would welcome a facility.Exsisting tracks have it tough because people really do suffer from nimby......good luck in your efforts.

Tom