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.
To think you have some mystic link into what black people will do over voting for Cain is ignorance, but the fact is if he peeled 5% of the black vote, obummer would lose bigger than moon-dale. If he lost 5 % of the vote and 5% stay home, he does not win in any of the 57 States.
Of course, there aren’t a lot of Jewish Republicans to begin with, but Bush got a higher % of the Jewish vote in 2000 than the GOP had had in 1992 or 1996:
http://www.jewishvirtuallibrary.org/jsource/US-Israel/jewvote.html
(Even after 9/11, Bush only moved up from 19% to 24% of the Jewish vote in 2004.)