Well, I think camaros are interesting cars. I seriously considered one when I was shopping around for my Mustang. What sold me on the mustang was the lower weight, the kickass coyote, the aftermarket availability, and general build quality... and the fact that it was super simple to get exactly the options I wanted from the dealer (trackpack, no tech package, etc). I also find them the most visually attractive, with the best stock engine noise.
The camaro felt roomier and more modern, but it was kinda boring to drive once you got over the whole 'I'm driving a Transformer!' schtick. The challenger just felt too damn big for a car that was supposed to be a pony car. The mustang had a live rear axle...and while that initially turned me off, I grew to respect that this iteration of the live axle was arguably the best one ever applied to a production car. I'd rather have the best solid rear axle setup over a somewhat mediocre independent rear suspension in the competition cars.
...for the money they ask for a z/28, it sure had better beat something! For that amount of money, go buy a new z06 and call it a day imo. Or, take the difference and build up your mustang - there isn't many production cars that will hang with a 35k mustang with 25K worth of aftermarket parts installed.
If I were you, wait until the new platform has a few model years underneath it's belt - go buy a new 5.0 in 2017. You'll hopefully avoid the kinks that come with a brand new model, and by then the aftermarket will be fully established. Who knows, maybe by then they'll announce the new Mach 1 or something