I don't think the slots or drilled holes are for cooling but rather to let the gases built up during hard braking escape which allows the pad to stay in better contact with the rotor for better stopping ability.
Or, I just made all that up because it sounds good. Personally, I thought the dimpled rotors I had on my old 93 Z28 did help the car stop better in adverse conditions. Bigger calipers/pads/rotors will probably help it stop better but at what cost is it worth it? It all comes down to what you're comfortable with spending your money on.