No...why would you not tune your car for new supporting mods? It only makes sense.
No, its not a waste...no matter what the temp the t-stat is the fans have to be tuned to turn on at a lower temperature. The GTP radiator is just fine for ANY modifications. Mine doesn't run hotter than 180* even in the heat...I don't know what is wrong if your car is. If you buy a bigger radiator then your wasting your money.