“Three years can be a long time in the life of a Broadway musical. Dialogue that once sparkled dims with routine. Performances grow soggy. Cast changes alter the chemistry that once made a show more than the sum of its parts. Even musicals forced into retirement well before a third anniversary can look prematurely aged by the time the last curtain falls. But as it approaches the end of its run on Dec. 11, after more than three years on Broadway, the Twyla Tharp-Billy Joel musical Movin’ Out is an improved model of the sleek, speeding convertible that vroomed onto the stage of the Richard Rodgers Theater in the fall of 2002, to become the most accomplished and most rewarding of the back-catalog musicals that have been washing up on New York stages like so much gaudy flotsam since the Abba gold mine Mamma Mia!“