Is there data to prove or disprove this?

I haven't given a shit about Apple marketing since I was a teenager, and I have bought many Apple products since then. If they could turn their marketing spend into a discount on the price instead I'd happily pay less. (Of course, this would reduce their sales, so it wouldn't work that way, but I'm not in it for the videos I've never watched.)

Obviously I'm aware they still have their fanatics, but how much of their sales is that really?