I also love my 5DmkIII but I have to agree the IQ is the same as the mkII.
What makes me love using the mkIII more than the mkII are the subjective things like the more robust feel of the body, the better rear LCD, the revised controls and most of all....the silent shooting mode. I also like the electronic level; a must for my architectural shooting. Oh yeah, the AF is waaay better and raises my keeper rate on my 70-200 f2.8 tremendously.
I had the optional focusing screen for the mkII that was supposed to aid in manual focus and found it entirely useless.
Live view is THE way to go but then you really need to be on a tripod. Of course when I use my TS-E lenses that's where I am.