It seems like a dubious musical mash-up: Broadway narcissists-turned-activists take over a middle-American town to help a lesbian teen who just wants to bring her date to the prom. But with a tuneful score, a playful book, and performances that remind you what Broadway heart and chutzpah are all about, this cause celebre of a show turns out to be a joyous, funny, and sweet production that should appeal to several generations of musical fans.

Bob Martin (“The Drowsy Chaperone”) and Chad Beguelin (“Aladdin”) wrote the lively, tender, big-laugh book — based on an original concept by Jack Viertel — for the musical that premiered at Atlanta’s Alliance Theater two years ago. It’s a 21st century “Bye Bye Birdie,” with showbiz interlopers causing havoc before finding their better selves — but re-imagined with a millennial slant and an echo of “Dear Evan Hansen” empowerment.

Leading this desperate group of career-slumping Rialto hams is Dee Dee (Beth Leavel, in a deliciously grand performance), who brandishes not just one but two Tonys to get a motel room upgrade. “How do you silence a woman who’s known for her belt?” declaims this diva, rhetorically, and pity those who would try.

Then there’s her co-star in their just-flopped musical “Eleanor,” Barry (Brooks Ashmanskas), who declares, “I’m as gay as a bucket of wigs,” and proves it by practically levitating out of his loafers.

Rounding out the quartet is the always-the-standby Angie (Angie Schworer) who shows she can still get a leg up on life, and Trent (Christopher Sieber), a clueless Juilliard actor/waiter whose non-Equity “Godspell” gig just happens to be bus-and-trucking near the problematic prom. Also along for the ride is long-suffering publicist Sheldon (Josh Lamon), who might not deliver Jimmy Fallon but can book a gig at the monster truck rally.

The locals include Emma (Caitlin Kinnunen, wonderful), the gay teen who is dazed and confused by the sudden attention she is receiving, as is her still-closeted and very nervous girlfriend Alyssa (Isabelle McCalla); their sympathetic principal Mr. Hawkins (Michael Potts), who turns out to be a big fan of Dee Dee (“Straight people like Broadway, too”); and Alyssa’s in-denial, conservative mom (Courtenay Collins).

Matthew Sklar’s easy melodies and Beguelin’s witty lyrics are a mix of classic Broadway show tunes (for the adult players) and exuberant or wistful pop songs (for the younger ones). Nearly everyone gets their musical moment or two, even as they may evoke numbers from other shows.

None are as designed for stopping a show as much as Leavel’s “The Lady’s Improving,” which she delivers with all the stops pulled out. But she’s not alone in capturing the spotlight. Schworer’s Angie goes for the gold when she spectacularly counsels Emma to get some Fosse-esque “Zazz.” Sieber shows his faith in the gospel of Broadway with a tireless “Love Thy Neighbor,” and Principal Hawkins, recalling Man in the Chair from “Drowsy Chaperone,” speaks for all showtune devotees when he lovingly sings to Dee Dee at an Applebee’s, “We Look to the Stars.”

Giving the show human dimension and heart is Kinnunen’s Emma, who has several moments of her own, including a lovely duet with McCalla, “Dance With You.”

Director Casey Nicholaw maintains his just-right touch in balancing the outrageous and the sweet, as he did in “The Book of Mormon” and “Something Rotten,” and then brings in dance numbers to show that choreography’s still alive and well and a hell of a lot of fun.

But for sheer Broadway bravura — that emotional moment so full of happiness that you think your heart is about to burst — nothing beats Ashmanskas’ exuberant song and dance of joy when he learns that he’s been asked to the prom at last, touching a chord in any kid who’s not only found a safe home in the world of musicals, but a little bit of heaven, too.