The idea of shifting the focus to Dr. Evil is a great one. There just wasn't that much left to do from Austin's perspective, but Dr. Evil has far more jokes. And I agree that for all its faults, the opening of Goldmember may be the funniest scene in any movie I've ever seen.
I can now report that ‘Austin Powers 4’ is indeed a go. Jay Roach would be back to direct the sequel. Warner Bros and New Line are partnering for this one, which has, quite secretly, been in development for a year now.