No it's not.
Blacks make up ~12% of voters.
Let's say that Romney speech at the NAACP pursuaded 1% of these voters. Romney just gained 0.12% of the vote.
Let's say he pursuaded 5% - He just went up 0.6%.
Let's say he pursuaded an impossibly unlikely 10% of black voters to move away from Obama and to himself. He gains 1.2% of the total vote.
Meanwhile, if McCain in 2008 had improved his standing with white voters by a mere 5%, he would have handily defeated Obama. And doing that for a Republican would be grossly easier than appealing to large numbers of black voters, who by and large hold diametrically opposite positions (as Romney just found) on economic issues than Republicans.
No offence, but minority outreach is largely a waste of GOP dollars. Sure, if they want to pump a couple million into it just to keep up appearances, fine. But I wouldn't put a whole lot into that kitty, if I were them.