Class racers are a unique group, for sure. The do have expensive cars, and they do mostly bracket race. Just to add to what you said, when they are paired against a car in the same class, it's heads up. Also, at some National events, they have class runoffs, where all individual classes are competed on a heads up basis. But yes, they mostly bracket race.
One class racer commented on another site that his machinist said he doesn't understand why he spends so much to go so slow. lol
I've always liked the concept, that of getting the most you can out of existing parts, but it has devolved for lots of reasons, a big one being how hard it is to get and afford the parts for a 60's or 70's car. Rules have changed too, they ain't as stock as they used to be. Later cars are run too, but they're not as popular for the most part. Exceptions would be later model Z28's Mustangs, etc. But they cost a bunch, too.