"Common" people have a perception that Mercedes makes the best cars in the world. They don't. People buy the Benz for status. And rich people buy AMG's because they're willing to pay an extra $40,000 for that badge, which their less-rich friend does not have on the back of his car.
Given unlimited funds, I'd maybe buy a CL or CLK AMG model, but I certainly wouldn't clean out a Mercedes dealer just because I can. Sure, they're great cars, but owning every AMG model on earth is overkill.
We all have lists of exotic cars that we'd buy if we had the means, but realistically, I'd probably just buy a few cars: let's say a Mazdaspeed 6 for around-town, a BMW M5 for showing off and going out with friends, family, co-workers, etc..., and something in the $200,000+ category for occasional fun.
Your comment about never setting foot in a Pontiac, Audi, or Mazda dealer is simply short-sided. Audi and Mazda make great cars that can be had for pennies compared to what you want. Pontiac's GTO is better than you seem to think, and is a real sleeper. Only those in the know have any idea as to what it's packing. That kid in the riced-out Nissan will go home crying as he sucks on 400hp from your bland family sedan. That's a major part of the fun, which you seem to be missing.
Enthusiasts like to seek out the car that's different and fresh, even if it means stepping into a Mazda dealer for the first time. You've chosen to adore Mercedes and Ferrari, the two most stereotypical "status" manufacturers in the world, while renouncing other brands as cheap imitators. Mercedes and Ferrari make excellent cars, yes, but have you really chosen them because of their merit, or have you chosen them because you want to hear people say "ooooh, that guy has a Ferrari!"
However if a GTO is your thing then more power to you, it's a much more attainable dream car then any of the cars I dream about. 
