The merits of sobriety in rock ‘n’ roll are long debated — better for the artist, sure, but for the art? When your favorite songwriter announces that, at long last and after many a broken-down stupor, erratic performance, fight with the wife, or 4 a.m. joyride over the neighbor’s mailbox, he’s finally kicking the bottle and the smokes in order to straighten up and fly right, you have every reason to be nervous.

When Jeff Tweedy, the 39-year-old frontman and mastermind behind the Chicago alt-country pioneer Wilco, said late in 2004 that he would enter a rehab clinic to overcome drug dependency, anxiety, depression, chronic migraine headaches, and a heavy smoking habit, his family and his friends were presumably thrilled and relieved. Many of his fans weren’t so sure … It wasn’t that we believed the drugs and booze were responsible for Tweedy’s sweetly melancholic music and comfortably abstract lyrics, but surely they helped make the man who made the best modern country and rock music of the past decade. We all suffer through life, and no one is better to do it with than Jeff Tweedy.

But it is the new and improved Jeff Tweedy and his recently expanded band who are offering their sixth studio album, “Sky Blue Sky,” this week. Upon first listen, the album is noticeably cleaner and more streamlined than anything Wilco has offered in years. Melodies are simpler, more direct. Lyrics are clearer, more precise. And the music, which sways in places, wanders in others, and stumbles from time to time, is clearly more of a collaborative effort among the band’s six members. No longer is Mr. Tweedy sitting alone in the studio with a half-smoked cigarette hanging off the main console, fiddling with effects pedals and splicing glitchy, twittering noises over the tops of his songs, as he did on Wilco’s last two records, 2002’s “Yankee Hotel Foxtrot” and 2004’s “A Ghost Is Born.”

But that doesn’t mean that Wilco has jacked the amplifiers to 11 and gone back to the full-tilt boogie and banjo soirées that marked its early work, either. Instead, Mr. Tweedy has focused his attention on the more polished avenues of the West Coast rock of the 1970s, particularly that of Neil Young and the Eagles. He has said that the common ground for the current incarnation of the band — which includes founding bassist John Stirratt, drummer Glenn Kotche, keyboardist Mikael Jorgensen, multi-instrumentalist Pat Sansone, and renowned guitarist Nels Cline — is the music made between 1966 and 1974, but listening to “Sky Blue Sky,” his attention is clearly fixed on the later portion of that spectrum.

“Either Way” opens the album with Mr. Tweedy delicately picking a tune on his acoustic guitar, but it’s only a few measures before the band arrives like an ocean ripple on the shore, quiet yet confident. The swell drowns out the country feel to Mr. Tweedy’s guitar and sets the band off on the path that “Sky Blue Sky” follows through most of its 51-minute running time: Mr. Jorgensen’s lilting keyboards float in and out of the distance and Mr. Cline’s slide guitar interjects a bowlegged saunter as the Wilco ship wanders toward the horizon with seemingly little direction but, nevertheless, lovely results. Were it not for the graceful and impeccable anchoring of Messrs. Stirratt and Kotche, however, one could see how the whole package might drift away. And the man with his hands on the wheel, Mr. Tweedy, sings with the wobbling optimism of the recently sober: “Maybe the sun will shine today / the clouds will blow away / maybe I won’t feel so afraid / I will try to understand, either way.”

The fuzzy, punctuated guitar lines that marked the more Neil Young-inspired moments on “A Ghost Is Born” make their appearance on the album’s second track, “You Are My Face,” but they are accompanied by their plodding, meandering brethren, which threaten to drag the album into the territory that many associate with the California sound of the ’70s, namely boring self-indulgence. Mr. Tweedy, with a bigger, more experienced band behind him, seems to feel the need to explore the broad, complex brand of music that was being made in his early childhood, but every step he takes into the extended guitar solos and harmonized bridges of songs like “Impossible Germany” and “Shake It Off” is another step the band takes toward the dreaded “adult contemporary” shelf at your record store.

Thankfully and not surprisingly, Mr. Tweedy, who was reared on the blue-eyed soul of country troubadours like Woody Guthrie and Hank Williams, and co-founded pop’s defining alt-country band, Uncle Tupelo, has not come untethered from his Americana roots. “Please Be Patient With Me” rambles down a country road and “Walken” hangs its hat on saloon pianos and more of Mr. Cline’s dexterous slide guitar. Wilco has come too far musically to leave anything unadorned anymore, but these simpler tunes, with their predictable progressions and lyrics (“I’m walken out by myself / I’m talkin’ to myself about you / what am I going to do?”) still offer the truest perspective into what made this band great to begin with and why it’s still great today.

With his 40th birthday around the corner and a new approach to life already in place, Mr. Tweedy seems to be searching for ways to reconcile his music and his psyche, which have always shared a small room in his head. He’s not there yet, but, like any recovering user, he seems to know that the passageway to the best music he’s ever written is a lot less hazy than it once was. “Oh, I didn’t die,” he croons on the album’s title track, about leaving home for an unknown future. “I should be satisfied / I survived / that’s good enough for now.”