Every now and then, a bubble of pure, tickling charm rises from the artificial froth of “Nice Work if You Can Get It,” the pastiche of a 1920s musical featuring songs by George and Ira Gershwin. Most of this show, which opened on Tuesday night at the Imperial Theater, registers as a shiny, dutiful trickle of jokes and dance numbers performed by talented people who don’t entirely connect with the whimsy of a bygone genre.