Mitt is awkward about this -- as he so often is -- but it's possible to tease out a grain or two of validity in what he says. First, part of what he was saying was that he ignored or alienated lower income voters. That much is true, and it did hurt him.
Second, "focusing on minority voters" wouldn't have done Romney any good, given Obama's massive lead among African-Americans, but if there's enough doubt among Blacks and Latinos about Hillary that some stay home or even vote Republican it would help the GOP.
So without seriously believing Republicans should "focus" on minority voters before other groups, it would be wrong to write minority groups (or less affluent Whites) off.
The grain of truth is that we should not assume minorities can’t think like conservatives. The mistake would be to assume that appealing to minorities means outselling the democrats with tax dollar goodies and low-life morals for minorities. That is not the way to appeal to them. Democrats will always win there. We need to convince them that conservative principles are in their best interest. Reaching out just means going where they go and making sure they hear the message and know they are welcome.