This is an age-old question that even a lot of successful promoters can't give a clear answer to.
I think there are three types of tracks now.
Legendary/Historical tracks - usually have a decent car count. Guys will continue to race there regardless of track conditions or payout cuz they want to be part of the legend. These tracks also typically host a premier division. (Ransomville, Canandaigua, Fonda, A-S, etc.)
Special Event tracks - get decent car counts because of the novelty of the venue, scarcity of events, or big crowd (Weedsport, Rolling Wheels, Little Valley)
Sportsman tracks - sometimes struggle with car counts, aren't as "polished" as the bigger venues, rely much more heavily on a local crowd both gates.
Obviously there are anomalies out there...tracks in their own little world that pull 150 cars or the flip side, gorgeous top shelf tracks that can't get anyone to show up. But for the most part, I think they fit into those categories one way or another.
Each track faces different challenges. It's been proven time and time again though, purses don't always bring cars. Racers are going to race where they want against who they want. If they want the best competition they'll seek it out, even if it's at a track that murders tires and pays poorly. Those racers are there for the glory and prestige. Then there's the weekly warrior...the local racer who races locally in front of his whole family and wants to be king of his home track. And finally, there's the sportsman racer who just wants to know that if everything went right for him one night, he might pull off a win. But he's not gonna spend insane money or make a ton of sacrifices to run up front. He's there for the ride.
The type of show you're running dictates who you'll get. If you're bringing in a tour or touting some race as the biggest and best, you're looking for the pro types. If you're running racing in a small community with lots of local support and don't need to rely on outsiders, you'll get your same guys whose family raced there for generations. If you're just putting up a sensible purse, don't have a ton of rules, and make it easy for racers to just show up, you're getting sportsman type racers.
I guess the point is you need to understand what your track is and who it can realistically draw then promote based on that. I've seen guys "get a deal" on a track, walk in, and honestly have no idea where they're at other than the point their GPS brought them to. Without understanding who your crowd is, and racers, you can't realistically set prices, rules, advertising, anything really. Just thinking as I type, I don't see a lot of fan (or driver) surveys taken anymore. I would think that would be some valuable information. Social media helps promoters connect and know what people want quite a bit more nowadays, but maybe some surveys would be helpful...if you could get the right people to fill them out.