$24K may be a little on the high side for a car with issues but the things you stated are not the worst. If it is mostly rust free, presents well, and all of the hard to find parts are there, the issues it has are not hard to fix. A new heater core, new carpet and a few new seals and those problems are gone.
Go with your gut (and all the information you can muster), If it feels good go for it.
Similar Camaros will always bring higher prices, that is just the way it is......but, Firebird people are more fun.