The Yeah Yeah Yeahs. (Dan Martensen)

The Yeah Yeah Yeahs spent their hiatus years working on tasteful art projects and high-concept operas. Fall Out Boy spent its hiatus years waiting to see if the members’ solo albums and reality shows took off before reluctantly deciding to get back on the bus. Both groups have returned from their respective hibernations with a heightened sense of nostalgia for their old selves and a renewed sense of their place in the world.

For a decade, the Yeah Yeah Yeahs have been haunting the margins of mainstream stardom. The group’s last release, 2009’s “It’s Blitz!” was a blatant attempt to seal the deal from a band that isn’t usually blatant about anything. An audience-friendly ode to the thump and throb of the dance floor, “It’s Blitz!” didn’t sell poorly, but it didn’t sell well, either. A blockbuster album “never happens if you try,” frontwoman Karen Orzolek recently told Billboard magazine. “So we’ve just stopped trying.”

Mosquito,” the band’s new album, is more complex and less danceable than its predecessor. It’s a darker, multilayered collection of art-pop songs incorporating elements of spiky punk, ambient pop, roots-inspired reggae, gospel, dub and soul. The album is filled with good songs done well, but “Mosquito” still feels as if it’s missing some ineffable thing. There’s a homogenized sameness to it, despite its disparate influences. And it can never quite shake off the art-rock chill.

On the great opener “Sacrilege,” Orzolek sings like a woman waking from a long slumber. (In a coffin, we’d like to think. Or a glass box, like Tilda Swinton.) Rousing and gorgeous, unusually uplifting (there’s a gospel choir), it’s one of the disc’s many fine songs, but the only true stunner.

Orzolek envisions being imprisoned by aliens (long story) on the crackling “Area 52,” sings over subway noises on the sad, literal “Subway,” and repeatedly struggles against her own overly minimalist songwriting, which relies too heavily upon words and sentence fragments repeated over and over. This can result in songs that are completely contained, perfect little universes (like 2003 hit “Maps,” which boasts a level of restraint and simplicity to which all Yeah Yeah Yeahs songs should aspire), but that too often merely sound incomplete.

“Mosquito” threatens to derail with the train wreck “Buried Alive,” which features overly busy production work from a no-longer-novel James Murphy, an appearance by rapper Kool Keith for some reason and “Space Invaders”-style sound effects. Things end well with “Wedding Song,” the group’s most unabashed love ballad since “Maps,” and the only song here that has as much heart as emotion.

Fall Out Boy, whose reunion was less certain, reemerges with “Save Rock and Roll,” the band’s first album in five years. If “Mosquito” suggests a band doing what it wants, “Save Rock and Roll” suggests a band doing what it must, although it’s still less perfunctory than the average check-cashing reunion release and often lands within shouting distance of its best work.

As on all Fall Out Boy albums, the eagerness to please, the air of tap-dancing desperation, the way each song comes out in tumble of words, is endearing, especially in comparison to the terse, regal “Mosquito.”

It helps that they’re kings of the overshare, with a soap opera writer’s love of expositional dialogue and Bruce Wayne’s sense of conflicted superhero obligation. Principal members Patrick Stump and Pete Wentz envision themselves as returning conquerors, ready to rescue rock-and-roll from any rivals who would despoil it. It’s tough to tell who they have in mind, since Emo Boys In Skinny Jeans Who Sing Catchy Pop-Punk Songs hasn’t exactly been a thriving subgenre since they left. “You’re wearing our vintage misery,” lead singer Stump grouses to whomever it is, on the great, clanging opener “The Phoenix.” “No, I think it looked a little better on me.”

Elsewhere on “Save Rock and Roll,” things are as they ever were. These are gleeful, pogoing singalongs, marinated in soul, disco and pop, and obsessed with the passing of youth, the pressure of fame and the encroaching suburbification of both band and audience. Once young mall punkers cavorting in sweaty clubs, they’re now “doomed to organizing walk-in closets like tombs,” Stump sings on the party-like “Where Did the Party Go.”

Divorce anthem “Miss Missing You” is the closest Fall Out Boy will likely get to emotive, Passion Pit-style electro (“Baby you were my picket fence,” Stump laments). Co-written with Wentz, it’s also probably the saddest, darkest Ashlee Simpson-related song ever. Who could have imagined a world in which Fall Out Boy was more cynical than the Yeah Yeahs Yeahs about marriage? Or about anything?

“Save Rock and Roll” ends with two cameos: Elton John gamely turns up on the title track, which is memorable mostly because Elton John is on it, and Courtney Love turns up on “Rat a Tat,” which is memorable because it’s discordant and weird. John’s appearance makes sense; “Save Rock and Roll” evokes the Technicolor carnival of his early ’80s work. But Love is a bad match, since Fall Out Boy only ever sings about Fall Out Boy, and Courtney Love only ever sings about Courtney Love, and they spend most of the track shouting past each other. Love is in gargly, Norma-Desmond-playing-Godzilla mode, chewing up everything — scenery, melodic structure, cigarette butts — in her path. For the sake of the song, which is awkward but not terrible, you just have to hope she eats Fall Out Boy last.

The Yeah Yeah Yeahs perform at Merriweather Post Pavilion on May 11 as part of the Sweetlife Festival. Fall Out Boy performs at Patriot Center on Sept. 10.