Do we get more out of theory than we put in?

The best measure of the value of a theory - in any endeavour - is how much we get out of it. The Governor of the Bank of England, Mervyn King (2005), has suggested that we could get more out of monetary theory, and I am sure that this is a frequent wish of all central bankers. But wishing aside, how much do we actually get out of monetary theory? And in particular do we get more out of it than we put into it? To address this question - which should be on the minds of all central bankers, thei