My preferred case as well. Used two different ones over the past year on my 5S, red and black. The new one for the 6+ is great as well.
Neither of my 2 leather cases showed any signs of the top leather flaking away.
Probably, but leather will almost always show signs of aging. My red leather case did change in appearance quite a bit but I expected that result going in. If someone wants a case that will be pristine in appears after longtime use, leather isn't you choice.
Disagree--the front of the space gray models is the best looking part of the phone--smooth black glass, very monolithic, with the ever so slight taper off the edge.
Included a few very quickly taken photos of my 6+ in the black leather case, as well as another of my favorite side of the phone.