Like to hear whether others agree or disagree with me.

I disagree. The market decides what the cars are worth. If the non-M cars are not worth the money, BMW would not be able to sell them. The premium price paid for M cars is just that, a premium over the non-M version.
My wife's 528 sport (non-M) is a better, more solid car in almost every way vs. my M3's. If anything I would say the M versions are overpriced, especially if you factor in the US dealer game playing/gouging/charging premiums over MSRP. My opinion.