I'd say Dylan's scathing personality is one of the main things that makes his music so great. In my mind you can't have one without the other....I love the way his cynicism and venom shine through on some of the older stuff, esp after he started turning it up. Clearly he thinks he's the smartest guy in the room.
Ballad of a Thin Man is good example......just love that song and that whole record.
Asshole, douche, shitbag, who cares. It's Dylan. Without him, well, who knows. I don't care how personable he is.
And as far as using one of Warhol's paintings as a dartboard, well he probably just increased its value a thousand times.