.. i hope to see more good comments and feedback on this thread and am eager to learn more about MS recording.
..however, i as you move more to the back of a room i assume there is a point at which a mid-side mic configuration becomes the wrong strategy because of diminishing returns from the side mic.
That depends on what you mean by diminishing returns. The side mic will still 'produce stereo' at a distance. It is true that the side component of the direct sound pickup becomes more and more diminished as you move farther away, but there is no reduction in the side component of the reverberant sound. In that way the sense of ambient 'stereo-ness' is not diminished, but the imaging of the direct sound is.
If you mean diminishing returns in the sense of how best to capture that sense of spacious reverberant ambience in your stereo recordings made from a significant distance, then yes, there are mic setups other than a coicident M/S array which many poeple feel are better suited to doing that.
For me its helpful to think of M/S as a good tool for optimizing the direct mono pickup of a sound source and 'stereo-izing' it. That is to say, the primary advantage I see in using M/S is in the ability to clearly choose the most appropriate directivity for the mid microphone and using that optimally, on-axis to the source. The mid microphone then collects side information to 'stereoize' that optimized mono pickup. In that light, I see M/S as placing primary emphasis on clear central mono pickup, then expanding on that to make stereo.
In constrast I see other non-coincident stereo mic'ing techniques as approaching stereo recording from the opposite perspective- starting from optimizing the stereo nature of the recording, then making sure there is a strong and clear mono image (which is not to say that it's unimportant or done less well, just addressed secondarily and less directly. Sort of working from the other direction.
Horses for courses.