Hmmm... lots of takers on this one.
Your last comment presents the conundrum: a 'nice' effect vs. phase shifting. Now, if you're a guitarist and need some cool phase-based effects, that's one thing. However, putting an entire mix through a phase shifter for the purposes of pseudo-stereo is likely to always produce the very experience you described, at least to a discerning ear: hollow. So you're not off in your description of the problem. I'm not aware of a good solution.
So the real question is more along the lines of what you're willing to do to the audio to create fake stereo. The nature of the recording is important too, because all pseudo-stereo processes are gimmicks, and some gimmicks fit specific styles of recordings better than others. You can do it by phase shifts (but mono summing just gets awful), narrow frequency band splitting (then your notes jump around at times), or by adding artificial ambiance (drowning in reverb no longer presents the original mix the way it was meant to be heard, but much of it will disappear when summed to mono). At this point in my life I'm accepting the virtues of virgin mono more than I did years ago and usually just leave it alone. The exception is when I can add some ambiance because it suits the recording nicely.
I'm no historian when it comes to the other portions of your question. Sorry. Hope this is helpful to you otherwise, David.
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