I saw about 30 minutes of the AEI’s Election Watch panel on CSPAN toay. It included Michael Barone, John Fortier, and Norman Ornstein. The part I saw (the last quarter or so) was dominated by Barone and he was quite good. He was a march of logic and full of facts, and some good insights. Quite interesting. Best analysis I have seen thus far. 
Barone is excellent.
Has Barone's character ever been maligned by the more partisan operatives on the left? I can't recall reading or hearing anyone make a disparaging remark.
Is he a rare "unimpeachable" center-right pundit?
Yes, he is unimpeachable, as far as I can tell. You can see why, when you listen to him talk about politics. He knows more than anyone in the room (including those sitting next to him on a panel) and there is never any flim-flam coming from him.