Music video games are hailed as possible saviors of both the video-game and music industries, but new figures show that appetite for games like Guitar Hero is falling away as entertainment spending slows. Variety.com reports that Viacom-Harmonix’s Rock Band 2 sold 809,000 copies last year domestically, while Activision-Blizzard’s Guitar Hero: World Tour sold 1.5 million units in the U.S.—both far below the franchises’ 2007 figures. Activision’s last installment in the series, Guitar Hero III, sold 55 percent more than World Tour. And games launched to cash in on the music-games market, perhaps most notably Nintendo’s Wii Music, have met with mixed reviews and even worse sales figures.

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Music remains the biggest-selling games genre and, according to NPD Group, brings in 16 percent of all gaming revenue. But music games overall saw a six percent drop in revenue despite some high-profile launches. Now with sales are slowing, revenue from extra tracks to play along to is of huge importance even though the cash is split with music publishers: at the cost of about $2 each, Guitar Hero players have bought 25 million tracks while Rock Band fans have paid for 30 million. Sales data for December is out on January 15 and will show how all the big titles did over Christmas. Activision (NSDQ: ATVI) is planning a Metallica-themed Guitar Hero for March while work is underway at Harmonix to bring a Beatles-themed Rock Band to shops for next Christmas.

Photo Credit: Bryan Gosline