Was there a significant number of ideologically convinced conservatives who stayed home because Romney was insufficiently conservatives, compared, say, to voters who weren't ideologically much of anything who stayed home because they thought he was a rich guy who didn't know about or care about ordinary people?
Instinct tells me that the second group was much larger, though I haven't seen any data one way or the other. The proportion between the two groups could indicate just what kind of Republican could win those stay at homes.
Ever see a list of states that have in the past voted for a conservative in greater numbers than voted for Romney in ‘12?