You get very close to the main reason I'm pulling for Obama. Hillary can pull in the Hispanic vote and that could be crucial in western states GWB carried.
I apologize if this is crude, but Hispanics will not turn out for a black candidate. It would hurt the Dems badly in the west.
(Of course, they might pick up some southern states on the strength of high black turnout)
Hispanics in TX in 2002 voted for black Ron Kirk for the U.S. Senate, but the whole Demo ticket lost.