i like to wrap sandpaper around old 1/4 round bar or plastic clothes hangers. to get down in places. or just have it sand blasted, starting at an aluminum oxide mix to remove all the main paint, then switching to a pure silica sand to smooth things out and save time with 1000-2000grit wet sanding.
i think a all polished motor would run a tad cooler than a stock motor, because there isnt any paint there keeping heat in. think nitromethane r/c cars, if the heads on those little motors are colored. they have been anodized, not painted.
i never did understand why yamaha painted the jug and dome on the blaster, when its an air cooled motor.