The emerging conventional wisdom that Romney is too “vague” on policy is somewhat misleading. The Romney campaign has some relatively detailed proposals on a number of subjects, but the real complaint about his “vagueness” is that Romney isn’t talking about them when he is campaigning. Many people expect Romney to behave like the technocratic wonk that he used to be, the person who once said that he wanted to get into the weeds of policy detail because “the weeds are important,” but Romney hasn’t been that person in public for a very long time. Romney cared about “the weeds” in 2007-08, and then he lost in humiliating, costly fashion. That’s why he doesn’t show much interest in “the weeds” this time around.
Jonathan Chait believes that Romney should "ignore conservative caterwauling":
Conservatives say they want Romney to change his staff or alter his campaign tactics. But what they really want is a different candidate and a different electorate. They want to believe that the American people are hungering for detailed endorsements of Republican plans to cut entitlement spending and taxes for the rich and launch a philosophical assault on the welfare state. But that’s not what the public wants and Romney knows it.
Bernstein takes a different approach:
[C]onservatives are quite right to push Romney for specifics — not because they would help him in November, but because specific commitments will tend to constrain him once he takes office.