As for Radiator Springs Racers, Disney just might experiment with new technologies that haven't been incorporated into Test Track. Nobody has said that the ride is going to be overtly similar to TT in any way.
Another thing, I've heard that the Little Mermaid seashell vehicles are going to travel in a suspended fashion - much like the Peter Pan ride. If they swivel like an Omniver too, this truely would be unique. I believe this is the ride vehicle that Disney was experimenting with inside the Peter Pan ride a while back.
Anywho.. I very much join with you in your excitement over Walt Disney Plaza. Perhaps we'll meet there in the future and become totally enamored by this first class trek to another time and place!