What does this week’s American Idol winner have to look forward to? Far less than in the past. The pop music market, now saturated with close to 100 of the show’s alums, is showing signs of Idol fatigue. Earnings for some of Idol’s top vocalists have nosedived over the past year. The show that reshaped television and the music business just isn’t minting cash for its stars like it once did.

Kris Allen, the 2009 Idol winner, has sold just 300,000 albums, according to Nielsen SoundScan. In the past year his music and touring sales have delivered an estimated $748,000—nothing much to sing about. He places 10th on our annual list of the top-earning stars launched by American Idol.

Jennifer Hudson’s light touring schedule and the end of her lucrative role as Avon spokeswoman hit the Oscar winner in the pocketbook, too. Forbes estimates that she earned $3.5 million in the year from June 1, 2009, to the end of this month, compared with $5 million the previous year. That dropped her to sixth place from second on last year’s list. Carrie Underwood, No. 1 on our list, earned an estimated $13 million over the past year—$1 million less than the year before. One Idol star, Taylor Hicks, didn’t earn enough to remain on our list.

Plenty of the show’s alums, including Hudson, have made money on Broadway. Among them: Clay Aiken, Fantasia Barrino, Ace Young and Constantine Maroulis. But Broadway shows are paying less, too. The salary of a starring theatrical role is now as little as 10% of what a newly crowned Idol winner grosses on a debut tour, typically about $300,000.

However, not all Idol stars are taking it on the chin. Kelly Clarkson and Kellie Pickler are in the midst of high-grossing, nationwide tours. Clarkson, No. 2 on this year’s list—and the very first Idol winner—made an estimated $11.7 million over the last year, more than double the year before thanks to a heavy touring schedule. Clarkson was one of the most frequently played artists on radio in 2009, according to Nielsen SoundScan. Pickler, No. 4 on our list, has played 100 concerts in the past year, bringing in $7.6 million.

But this season’s stars probably won’t do as well. If there’s one thing lacking among Idol contestants this year, it’s an “It” factor. Neither of the final two vocalists—24-year-old musician Crystal Bowersox of Toledo, Ohio, and 24-year-old paint sales clerk Lee DeWyze of Mount Prospect, Ill.—have the personality draw of, say, an Adam Lambert. And so far there has been little personal drama in their rivalry, unlike David Cook and David Archuleta (season seven), who battled each other like musical gladiators.

Adding to this lackluster season may be an Idol backlash, of sorts. Blogs that cover the show suggest its aggressive product promotions are turning off fans (a recent episode plugged Ford and the latest Shrek movie in back-to-back video segments). There is less behind-the-scenes action to chatter about. Gone are the wacky, off-camera antics of former judge Paula Abdul, who left the show last year. Idol’s creator and its central personality, Simon Cowell, is also leaving after the show’s finale Wednesday night.

Idol now averages 24 million viewers a broadcast, down from its high of 31 million in 2006. A Frank Sinatra-themed episode in early May that featured a special appearance by Lady Gaga drew one of the show’s lowest ratings ever, dipping to 17.5 million viewers. Worse, Idol was recently overtaken in the ratings for the first time by ABC’s Dancing With the Stars.

All that said, Idol is still among the most lucrative shows on television. During the upcoming finale, Fox is believed to be charging $1 million for a 30-second spot. The network reportedly pays Cowell $30 million annually for his judging, far more than any Idol contestant has ever made in a year.

Celebrity performers who appear on Idol do so to tap what is still a powerful promotion machine. In May, after Lady Gaga performed a new song, “Alejandro” (wearing a black thong and fishnet bodysuit), sales for the single jumped, says Nielsen SoundScan Vice President Chris Muratore. “The airplay Gaga got of that single was astounding. Digital sales of “Alejandro” went up 70% after her Idol appearance, from 78,000 to 133,000 per week,” he says.

Bowersox and DeWyze will no doubt be signed to record deals, but no one is betting either will be the next Carrie Underwood. That leaves viewers to ponder the show’s only true dramatic storyline this year: Can Idol survive the departure of Simon Cowell, its most recognizable presence?

One viewer believes so. “I think Simon is a kind of love-to-loathe character who revels in his ambiguous popularity,” says Ellis Cashmore, author of Celebrity/Culture and a professor at England’s Staffordshire University. “But American Idol is too robust to suffer from the loss of one individual.”