Do what you want, it's your money.
BUT, you are going to have to yank GNX parts to replace with other stuff to make it run what you want. Once you yank this stuff, you basically have your run of the mill Turbo Regal. So, why do it with a more expensive starting point, when you can do it with a cheaper model, and have more money available to do it with?
Me? I prefer to drive my cars, and mod them the way that I want, which is why I won't ever buy a GNX. I would want to drive and mod it. Unless of course I hit the lottery, then I would buy two and put one on a lift and drool on the floor while looking up at it, and mod the heck out of the other.
Brian