I don't think Republicans will have to do much of anything honestly. They will not get much of the black vote just by virtue of who Obama is - unless he pulls a Michael Jackson and tries to become white or changes his nose size.
As far as Hispanics go, there are a lot of them here legally, and many of those folks don't support illegal immigration (without some form of control) either. It affects them in negative ways as well. Otherwise there are plenty of moderate "Asians, working/middle class Northeast/West Coast/Midwest whites" that are going to basically say enough is enough with all this government spending. You are also seeing a lot of States pass resolutions on their 10th Amendment Sovereignty rights
http://www.wnd.com/index.php?fa=PAGE.view&pageId=104524
and if the Democrats in Congress don't figure that out, they will set themselves up to be defeated.
I would not count on Palin being the nominee - I think Romney will get it if he takes a serious run at it. The whole "He's a Mormon - gasp!" issue is out the window since we now have Obama who professes to be Christian but embraces Muslims. A Mormon will look tame in comparison.