Not much, like I stated before. I didn't say none. I said few. I have many dirt bikes and cars all with shop manuals. Aluminum without a backing nut does not hold a lot of torque. It would have to be a bigger bolt with thick threads to torque more.Look on an all aluminum engine, lots of torque specs beyond 15 ft lbs on aluminum threaded holes.
I’m not saying galvanic corrosion isn’t a concern for many fasteners, but a zinc plated fastener in an aluminum internal thread is not a big corrosion concern. Especially in a dry, fairly well sealed application like a spark plug. It’s actually better from a galvanic potential standpoint than a zinc fastener in a steel internally threaded hole.