I agree it mostly hurts more than helps. I do think Joe Biden was a help to Obama - moreso in 2012 than in 2008 (he would have won no matter what in 2008), although Obama's aggressive campaign against Romney was the biggest help, Biden was pretty solid and was a good contrast to boy wonder Paul Ryan.
I have a feeling Hillary and her people are panicked over Trump likely cutting deep into what's left of the blue-collar white vote in places like the Midwest. I can understand why, but I'm not sure of the choices. I do like Tim Kaine, and he seems to know how to win tough elections, but his views on abortion are going to upset some, and he didn't exactly set the world on fire in his post-SOTU address back when he was elected governor. Vilsack was popular in Iowa for a certain amount of years, but I don't even know if that's the case now. And wasn't he a part of that huge ugly mess against Shirley Sherrod? I think he'd be a minus.