I don't know heaps about the Gold Coast. It's got a bit of a reputation for being full of bogans, but it's also got plenty on offer. It's got the theme parks and the beaches are lovely. If you're in Brissie you may consider heading the other direction for a few days and going to Noosa and Fraser Island. It's really lovely up there. The hinterland around Maleny and Montville is also picturesque if you're into arts crafty sort of stuff.
Depends what you want to do really. I prefer quieter places with walks and nature and beaches and good food. If you want more "action" then the Gold Coast should be fun. I've been to Movie World which was quite fun. It might be too cold for Wet N Wild though. It's not far down to Byron Bay either - that's a lovely spot to hang out for a while. I haven't been, but I hear Lamington National Park has some beautiful walks etc.
I've never really spent time in Brisbane either so I can't give you much info on that city. Again the stuff just out of Brisbane is meant to be good. I've heard good things about Stradbroke Island - probably closer to the Gold Coast too.
