Anytime you increase wheel weight, or mass, you'll increase the amount of power needed to turn them. There are superlight big wheels out there, but I don't know enough about their strength to recommend them.
Another downer is that it also takes more braking power to stop the car with bigger wheels. I'd recommend Cobra brakes too.
Don't know what you're doing with your car, but you could run the big wheels around town and keep your stockers for playing at the drag strip.
The main reasons the factory put the small rims on there were 1) cost and 2) acceleration/braking improvement in the weaker drivelines. They figured if you wanted the really good looking wheels you'd buy the GT or Cobra, I guess.