I think it is far to say that a GTI or R is one really nice car, cost included or not. I've had someone say my interior looked nice enough to be in a Lexus. That's high praise! And with a simple Stage 1 tune both the GTI and R become very quick cars.
With that said, throwing in cost into a debate about cars is completely logical, but always leads back to the simple fact; People pay more for a BMW, Porsche, Aston Martin because they want all the things that come with owning a luxury brand. Like being able to own 1 of 740 cars sold in the USA, or 4 years / 50000 mile standard warranty, or being able to pick the color of your seats and interior trim, or ... list goes on and on. The point is, yes, money can make a GTI, Golf R, or Mustang crazy fast, but they will still not be a BMW, Porsche, or Aston Martin.