MGM really does need a new E-ticket... it's been just over 7 years since Rock 'n' Rollercoaster opened. Over 12 years since Tower of Terror! I'm sure the car stunt show is nice, but like most shows, it's a one-time viewing, and you're done until your next trip to WDW. MGM needs attractions, not shows!
In the last 7 years, Epcot has gotten Mission Space, Soarin', lots of new stuff at the Living Seas, upgraded Imagination ride... AK itself is just 8 1/2 years old, and has gotten a huge E-ticket ride recently in Expedition Everest. The MK hasn't seen much in the last couple of years, but it's already a fully fleshed out, multi-day park that doesn't need help (and even it has gotten Pooh and Philharmagic - I'll ignore Stitch's Great Escape for now).
MGM... it was puny when it opened in '89, and there was a mad dash to add rides and attractions. In my opinion, it's really only got a handful of repeatable attractions - ToT, RnR, GMR, and Star Tours. Everything else is a show, tour, or exhibit - one viewing and you're done. Honestly, GMR and Star Tours aren't that repeatable for me either...
I think what it will take is AK's attendance numbers to overtake MGM, before MGM really gets a hard look and some money. Seeing as the 2005 attendance numbers were 8.2 million for AK and 8.6 for MGM (and that's with no EE at AK), I wouldn't be too shocked to see MGM come in 4th for 2006.