You might have a look at the Huffpost Senate charts. At least four races look fairly close to me: NV, NH, NC and PA. The ones you identified. And isn't Wisconsin/Feingold a likely Dem recapture?
http://elections.huffingtonpost.com/pollster#2016-senate-races
Sam Wang sees it as most likely 50-50, which gives a useful role to the Veep.
http://election.princeton.edu/