I have a big problem with the replace both gears because of noise practice. The crank gear is steel, cam gear is aluminum. Since the aluminum is considerably softer, wear on the crank gear will be negligable. The cam gear will wear to match the crank gear, whether it's new or old. I recommend putting on a new cam gear, every time it goes on or off it loses some metal and has that much more reason to come loose. And as for heating the aluminum, don't get it red and let it cool at room temperature. Keeping it below 500 is a good practice, but if you are heating the gear and not the cam it should drop off long before you reach that temp.
A lot of the older shops kept a hot plate for the aluminum gears. Didn't take up much room, worked pretty fast, very little maintenance, and they were cheap.
