Haha, Republicans keep hoping minorities voted because of Obama's "demographics". A landslide is coming folks.
There is some truth to it, at least with African-Americans. Though I doubt there were many otherwise conservative blacks who voted Obama solely due to race (as closet racists like to crow about), the idea of a black president clearly got many non-voters to turn out; black turnout in 2008 and 2012 was much higher than in prior years, even if Obama didn't do exceptionally better percentage-wise than Gore and Kerry did. In 2016, the black vote will obviously remain ironclad Democratic, but the depressed turnout will probably keep NC and GA red and possibly swing back Virginia and even Ohio.
How much, if at all, did black turnout increase as an overall share of the electorate, compared to their overall demographic share of the general population? Black turnout increased in 08 of course, but increased across the board for almost all demographic groups. I seem to recall reading that the black share of the 08 electorate increased from 04 only marginally more than the general population's increased % of blacks from the same time period. I also vaguely recall being corrected on that point on the Forum, and now can't remember which is correct.