I vote for Hornets, Hobby/Street stock and Modifieds as regular classes. These will get the highest car counts and are the most affordable. I love Late Models and Sprint cars, but to be affordable they need to be a crate motor class in my opinion. I have watched the Crate Late Models race at Ocean Speedway in Watsonville, Ca. and they are plenty fast and put on a great show. Also there is a touring series based out of Oregon. I think a Crate moter Wingless Sprint Car class would be a great class also. They run a class like this at many tracks in Ca. only they are cast iron 360ci. with a 2 bl. carb on alky. Every thing else is pretty open. Lots of cars at every track they run at, but still a pretty expensive motor. Also there is no need to make the Sprints run expensive or complicated clutch setups. The cars are so light they just need a flexplate, starter and a battery and they start up and take right off.
I think that you are correct. You could have those particular classes as a regular show, and slowly integrate larger races in a couple times a year. Soon, it will take off and everyone will be racing dirt! I know my dad has a killer dirt modified that is just sitting, and there are several others in the valley. Your on the right track i think!