I've seen Dylan about 8 times, and every time his performances were COMPLETELY different. But that's the nature of a Dylan show - different set list every night, different song arrangements, etc. It makes things very interesting. Some very magical things happen that way, and some not-so-great things happen that way. Paul Simon is the complete oppostie - TOTAL PERFECTIONIST. I was shocked when they said they would perform 3 songs together at each show given how different they are - but it worked. I especially liked the oldies medlies they did. (That'll be the Day/I Walk the Line/etc.)
Just because people don't like each other doesn't mean they can't make good music together - case in point: Let it Be, White Album, and Abbey Road. Great moments on those albums despite the anxiety.
As for Simon's post S&G output: It think it's great. In fact, I think in many ways it surpasses S&G as a whole. (It's much more experiemental, etc.) I think Paul Simon, Still Crazy, Graceland, Rhythm of the Saints, and even You're the One hold their own against any S&G record. The point is, they are 2 entirely different animals. S&G was about mellow tunes and angelic harmonies. Paul Simon solo is about experiementation.