Related item: Ross Douthat has a great post on why Romney picked Ryan as his VP choice. Douthat identifies a key weakness of the team when it comes to appealing to economically strapped middle class voter:
[It] is the (understandable) fear among hard-strapped voters that Republican policies will benefit the rich more than the middle class. Ryan’s association with entitlement reform is at best orthogonal to that weakness, and at worst it exacerbates it substantially.That's spot-on, I think. The Romney-Ryan ticket has to make a convincing argument to the middle of the country that their economic proposals will be better for the middle class than the current trajectory of the country under Obama administration.