Hmm, maybe I'm the only person, but I absolutely adore this game. You guys should play it before throwing it off as a senseless clone, there are plenty of things unique about it. Beside that the story mode is adorable and hilarious, Mog is the biggest jerk ever. Anyway, the secret characters include cactuar, moomba, Squall, (Aya Brea is just a police car), Cloud, Airship, Classic Chocobo, Jack, etc.
Personally, me and my ex-girlfriend had loads of fun with this game, we played all the time when I first picked it up, got all of the secret characters, all of the ending videos, and made an ultimate racer. Which I might add is also cool that when you beat the game, depending on how well you did, you can make a custom racer attributing the stat points you earned to his/her racing stats.
Anyway, magic stones were an excellent idea for powerups, makes the game really fun, among other features. Chocobo Racing is an altogether good game, if you play a game looking for how similar it is to another game you might never be satisfied.