-- that no one probably wants to hear. But it's this:
Run some races at the short paved ovals... like the USAC Midgets do. Midget racing has supported itself and run continually since the 1930s with only one break -- for WWII.
The reason the oval shows work and (lower level) pro road racing doesn't, is that a short track attracts the paying customer. It attracts him (and his family) becuase he can see the whole show from his seat in the grandstand, get a cold beet and some warm food just a few feet away, and have an announcer tell him all the exciting things that are going on.
It's the oldest formula in the books. And heck -- at some of the longer (5/8ths and up) tracks you could use the infield and put on a little road-course show.
I've wondered for years why no one's tried putting formula cars into the Saturday Night Under the Lights milieu. I know it ain't very Grand Prix in feel... but it sure would pay some of the freight... and make formula car racing in America something more than just a damned expensive hobby.