Hi Robert,You could look at the M vs SL question in a sort of philosophical/psychological way. And which you might go for depends on your style and, in a way, who you are.
The M could be better suited to the 'introverted', contemplative person; someone who is prepared to wander around until the best view of whatever it is comes into view; using the 'foot-zoom' rather than the optical one; someone prepared to wait for the opportune moment.
The SL might be better for the 'extroverted' spur-of the moment person; someone who seizes an opportunity, and fires away.
I'm not so sure how far I can push this argument; the M might well be better if you want to get up close and involved rather than being 'stand-offish'; a participant rather than an outside observer. That would reverse my initial arguments, for the participant would be 'extroverted' and the observer more 'introverted'. But then, perhaps you do both at different times.
interesting thought. The participant vs observer -IMO-depends more on the focal length than on the body. Even though the optical rangefinder maybe gives a more real feeling to the photographer than the EVF. Overall I agree with you that the M has allways been a camera which makes it easy to get close into the scene. But the SL with a small 35 or 50mm prime isnt bad either in this regard.
I think its cool how small the excellent 35/1.4asph or 50 Summicron (no matter if APO or non APO) are, if you look at comparable DSLR lenses.