Interesting article- also interesting, because it brings up intersection of music and engineering. In most musical instruments and voice, "good" overtones are highly sought after, as they give color and projection. Leo Fender & Jim Marshall built their amp companies on "pleasant" distortion. Guess most would agree that the purpose of reprduction equipment is to reprduce accurately, not add or take away from what's in the mix, but like you say, in some instances in the mids, the speaker can help make the sound a little warmer and smoother if the harmonic distortion is truly "harmonic".