The ending of Austin Powers in Goldmember resolves the meteor plot by making Austin and Dr. Evil, who turn out to be brothers, reverse the tractor beam together. Goldmember starts the beam, Austin and Doug (Dr. Evil's real name) reverse its polarity, the meteor is destroyed, and Goldmember is arrested.
The story is then shown being adapted into a movie, and Austin and Foxxy kiss after a screening of it. Scott, now bald, vows revenge. During the end credits, Mini-Me is shown talking with Britney Spears. That is an end credits moment, and no separate post credits scene has been verified.
Why does the brother reveal matter? In my opinion, it is the smartest structural move in the film, because it turns a rivalry that began in 1967 into a family argument. Nigel Powers is the kidnapped father the whole 1975 chase is about, and Dr. Evil spends the series at odds with his own son Scott, who wants nothing to do with him in the first film. Making the hero and the villain share a father lines those threads up, and the team up to reverse the beam is the payoff.
The film within the film is a Bond style joke, since the saga parodies the James Bond films. It could be argued that it is also a neat way to say the story is over. Scott's vow, meanwhile, perhaps leaves one thread open, and the status of any fourth film is covered on the Austin Powers 4 page.