Polls indicate that McCain is losing the African-American vote 93% to 2% and losing Hispanic-Americans 58% to 31%.
Frankly, pursuing African-American voters with a large share of his campaign resources would be a tremendous mistake for John McCain. Even if he managed to completely negate Obama's natural advantage, and achieve the same margin that Bush did in 2004, he would get 11% of the African-American vote. Link
Some would argue that Condi Rice could be a factor in that, but let's not forget that Alan Keyes couldn't even hold his own party's support against Obama in 2004- he only took 27% of the vote in Illinois, and 8% of the African-American vote. Link
Part of the reason may be an understanding by minority political organizations that reciprocity from their party is more advantageous than actually having leaders of their own color, not to mention the democratic leaning of many such organizations.
The Congressional Hispanic and Black Caucuses have each at various points withheld their support for members of their own respective races challenging democratic incumbents, in the interest of currying favor from the Democratic Party, and instead devoted their resources to running minority candidates in "safe" republican districts. In essence they settle for a long shot rather than rock the boat. Therefore although the individual voters may be more open, the network of contacts and resources which drive popular culture and the media do not kick into action to capitalize on that openness. This has benefited Barack Obama in races against African-Americans with more conventional "Americanized" images. The relatively low impact of the occasional allegation that he is out of touch with mainstream African Americans can perhaps be attributed to this.
Interminority Relations in Legislative Settings: The Case of African Americans and Latinos (See Page 19)
What Condi Rice really has going for her is how popular she is with women and Republicans. Open-ended poll questions found her to be the 3rd most admired woman in America in 2007, behind only Hillary Clinton and Oprah Winfrey- neither of whom are likely to run with McCain. That popularity also extends to independent voters according to the poll.
Rice isn't just personable though. People think highly of her professionally. She generally maintains a favorable job approval rating with the majority of voters, even when President Bush is setting record lows.
2006 Approval Ratings
On a more upbeat note for the GOP, a 60 percent majority approves of the job Secretary of State Rice is doing — far more than the one in five who disapprove (22 percent). These ratings are consistent with previous results.
Condi Rice is good for McCain with the Republican base, and good with women and independents. All in all that makes her a very strong Veep candidate, especially compared with candidates who appeal to the religious right, since McCain is already winning by just under 3:1 with voters who attend church weekly. Link
What is less clear is how Rice would do with Hispanic voters, who McCain does arguably have a shot with. Although he could probably do without them in a lot of places, he will be glad to have their support in Florida and Colorado at the very least, if he can get that support.
There is some racial tension between Hispanic-Americans and African Americans. I say this as someone who grew up in schools that were majority black and hispanic, and who witnessed "black vs brown" race brawls on many occasions.
By taking Rice, McCain sacrifices the ability to play dirty on Race in the Spanish-language press (using local print ads paid for by surrogates to raise questions about whether a black president can be trusted not to forget immigrants while seeking change for African-Americans). Forgive me for being cold and calculating because I certainly don't condone such conduct, but that is a play that could help McCain.
Also, McCain may stand the most to gain among Hispanic voters by appealing to their basically conservative cultural values. A catholic Veep could do that for him. Mel Martinez of Florida comes to mind- although they'd have to hire a REALLY big staff so he'd never run out of people to blame for leaked memos.
So Rice and Martinez look decent, and of course there's Pickens as I've mentioned earlier, although that one is getting more and more distant- he was at the Democratic convention today and there's just not enough time to thoroughly vet him if they haven't already at least done some basic homework.