If Wisconsin votes for Trump, it will be because of him, not because of Gov. Walker. Walker does not have high approval ratings and barely won in ‘14 (a good GOP year) against an execrable Dem nominee. Fact is, VP nominees tend not to particularly help Republican candidates from Dem-leaning states. Ryan (WI) didn’t help Willard, Kemp (NY) didn’t help Dole, Agnew (MD) didn’t help Nixon (’68), Miller (NY) didn’t help Goldwater, Lodge (MA) didn’t help Nixon (’60) as examples.
I think you are right, lets try not to outsmart ourselves and be cute with the VP selection. Both of the Bushes pick somewhat unknowns and they won.