Image quality, LS vs non-LS, optically the newer Phase One Schneider LS lenses are overall better, and about 3x or the cost. This is glass.
Leaf Shutter vs Focal plane, to me is moot unless you need the higher flash sync, remember the DF+ or DF both will be firing both shutters, i.e. the focal plane in the camera body and the Leaf shutter in the lens. So you still don't get rid of the possible mirror shake, which I always found a bit harsh on the DF or AFDIII especially when the camera was in the vertical mode.
If you look at the Digital D non LS vs. older Mamiya AF versions of the 35mm, 45mm, (not sure how many more there are that are non LS) the groups and elements are the same so basically re-badged. The LS lenses are all new designs (except for the 28mm) which has the same number of elements and groups as the older 28mm. (Phase One or Mamiya)
Still hoping to see a firmware update to the DF+ or DF that allows the focal plane shutter to be moved up and out of the way when using the leaf shutter lenses.