I've seen DT 9 times in various locations since 1993 - the upcoming show will be my 10th. The majority of the time, James has sounded great. But at the last show I saw last year - yech. Oh, I was so disappointed. He kept shouting instead of singing. I'm crossing my fingers that he doesn't pull that again on this tour.
As for meeting bands afterwards, the DT guys have been universally nice to me, though it's rare that I'll run into ALL of them after an individual show. The night I saw them in London, John Myung came out the stage door and was clearly in a hurry, and some guy *chased* after him.
John was gracious enough to stop and sign something for him, and then a bunch of other people started collecting around him. I try very hard not to pester people if they look like they're busy; it's not the end of the world if I don't get an autograph, handshake, hug, whatever, from a particular musician.
SX have always been very nice guys too, the two times I've been around them.
I've never had a bad experience meeting anyone, really. The only person I was ever totally disgusted with was Stephen Pearcy, and that was for his obnoxious behavior onstage with Arcade, and they didn't even stick around after their set...