“Dreamgirls” so seductively traces the steppingstones of the group’s ascension, masterminded by cold, calculating Curtis Taylor Jr. (a suave Sydney James Harcourt), that you tend not to notice that Tom Eyen’s book sort of peters out toward the end. (The awkward reconciliation of Effie and Deena Jones, the Diana Ross character played here by the splendid Shayla Simmons, has never felt particularly convincing.) Krieger supplies much worth listening to, in pour-your-heart-out melodies and clever lyrics for the Dreams’ and Early’s songs that often convey deeper, offstage meanings.

Signature wants the eye, too, to be delighted. So on the girders and platforms of Adam Koch’s multilevel, hydraulic set, lighted with concert-hall aplomb by Chris Lee, Gardiner allows costume designer Frank Labovitz to let out his own inner Bob Mackie. The Dreams change costumes at the speed a Metro turnstile processes SmarTrip cards; each singer — vivacious Crystal Joy as Lorrell Robinson and solid Kara-Tameika Watkins as Michelle Morris fill out the group — has something like 20 dresses to get in and out of over the course of 2¹/₂ hours. The gowns of aquamarine iridescent sequins Labovitz designed for the title number — a creepy/sexy song suggesting the young entertainers as geishas — glitter like Caribbean reflecting pools.

The ambitious scaling up of the glamour factor — even getting on the ever-evolving wigs seems a military operation — helps to define the progress of the Dreams, who in Eyen’s telling are shoehorned into public images they can’t sustain. Labovitz’s contributions here are not only wonderfully executed, they are essential. (Watch for the witty onstage quick-change he devises for Payton in Act 2.) The sleek sleeveless and one-shoulder gowns in which he drapes the Dreams suggest Motown goddesses; as the fissures open up among the women, the era-mirroring outfits of the ’60s and ’70s become ever flashier, and, in a way, sadder. Ultimately, the dresses forlornly seem to be wearing the Dreams.

Like so many great Broadway musicals, from “Show Boat” to “Gypsy,” from “Follies” to “A Chorus Line,” “Dreamgirls” is an attempt to draw back the curtain on the turbulent lives of show people. It’s focused more than those others on the business side; as foreshadowed in the cool, silkily choreographed production number “Steppin’ to the Bad Side,” Curtis must grease palms and sabotage competitors to clear the group’s path. The manipulation gives a cynical spin to Krieger’s wonderfully ironic “Family,” the song Curtis, Effie’s songwriter brother C.C. (the endearing David Bazemore) and the other Dreamgirls sing to Effie to console her after she’s been dumped as lead singer.

The moment Curtis informs the entitled, untamed Effie that he’s pushing her to a supporting role in the group is a crucial one, and one for which Signature’s impossibly wide main stage is perhaps not ideal. Payton’s back is to much of the audience as Curtis delivers the devastating blow. It is frustrating to miss her expression, denying by some important fraction our desire to commune with her.