With Pomerantz and his winning company on board, Vanities-The Musical nonetheless remains not only diverting but endearing, right up to the feel-good conclusion that Heifner and Kirshenbaum have provided. Heifner’s play was never a searing piece of social commentary to begin with, and by continuing to brighten both the presentation and the resolution of this spinoff, he’s giving his nearly 50-year-old baby room to grow.