My speakers routinely create the illusion that sound is coming from positions wider than they are, as well as positions between them. I normally sit in an equilateral triangle with them, and they are about 8" apart (yes, an ST joke). I suppose this illusion is good as it suggests that they are making a fair fist of recreating the stereo field with little distortion.
However, stereo effects hold little musical interest for me, and I would be quite happy with a mono system if it were as detailed as the equivalent stereo one. That is seldom the case, since some distortion is asymmetrical, and the ear hears two separate recordings as more detailed than one. The same thing happens with stereographs, which appear more detailed than their film format would normally be. I think stereo was a saleable gimmick which had the accidental benefit of reducing perceived distortion and increasing perceived detail, so I agree with Mr Pig that the effect of speakers disappearing is unimportant to enjoyment of music.
