Running the heater will pull some heat off the engine but I think with what we are typically running as far as power and the heat generating capabilities of our cars, it doesn't make that much of a difference.

As far as cooling the car after the run.......shoot yeah, blast that heater with the key in the acc position, and every now and then crank the engine over for a short period to cycle the coolant through the radiator. Also, do the smart thing and put a constant on switch to your fan. That is by far the easiest way to make your car run cooler. And while we are on the subject of coolant, make sure you are bypassing your throttle body coolant inlet thingee. You guys might be able to explain better.

As far as the water mister for the radiator and crap, probably not as efficient as the NOS nozzles you see spraying down intercoolers but I cant imagine it hurting.......so why not. Pack some ice up in there and blast away.