There are a million things you can learn from a plug but you have to do like above and run a brand new plug, full power if the plane can do it and then keep the throttle full open and kill the ignition. You will need good eyes or a scope. You can do all this and chase readings around and eventually end up back where you are now. If it sounds good, turns good numbers and reliable then dont mess with it. If you are looking for more power then get a bigger engine.