With talk of a significant update to SDSC coming (Parkz interiew with Clark Kirby), I was thinking.. the previous version of the ride I interpreted as Scooby getting so scared, he runs away from the haunted castle ride and the gang joins him at a party* instead.
I'd kinda like to see a more involved plot, where they catch a monster and reveal the villain. So in the queue you get a story of a monster and meet a few characters who set the story up.
The part of the ride up to the elevator is Daphne, Fred and Velma decide to go one way, Scooby Doo, Shaggy and you go another. The elevator is a trap the monster sets, and the wild mouse element is a chase scene you often see in the tv show, where the monster chases Scooby and Shaggy.
The turntable and hairpin corners are you avoiding the monster, with audio in straights of Fred, Daphne and Velma setting a trap for the monster. You catch the villain and reveal their identity before the 'surprise drop'. Maybe keep the MXPX music for the disembark station/walkway to the gift shop.
* Unless the wild mouse section was always meant to reference a 'chase' scene?