John... I wouldn't begin to argue against your experience. I feel this to be true though... most if not all really small home studios are not treated correctly or even close and the owners have made the situation even worse by dividing the volume further. Of course, I have no way prove my point, but I know my experience with treating small rooms, and it's no easy chore.
I do know this, my larger room has required significantly less treatment. It's not where I want it to be, I'll probably never be satisfied totally... like my recordings, but the separation and imaging was immediately perceivable.
Everything involves tradeoffs, and I've found that the tradeoff of separate smaller rooms for monitoring during tracking does not outweigh the benefit of a better tracking room and better room for mixing.
-kp-