The VP slot generally does a very poor job of pulling in new voters. (Palin may be the exception that proved the rule.) And that’s usually how even something as positive as a Reagan Revolution gets diluted by the follow-on of Bushian big government.
Palin actually brought a chunk of female voters, but Obama brought more youth and black turnout than we could match.
Lieberman brought a lot of Jewish Republicans to the Democrat column in the 2000 election.
You can make a difference there, but you have to choose wisely and choose movable demographics.