Believe it or not but I'm having alot more fun with this game than with MarioKart DS, I haven't played MK DS online yet so maybe that's why. Here are my top scores:
Multi Mission Bounty: 2,408,750 - 10
Pirate Frigate Bounty: 579,700 - 02
Tallon Overworld Bounty: 2,463,550 - 07
Phazon Mines Times: 1:37:39
Phendrana Drifts Times: 1:30:55
I haven't unlocked the other 2 stages yet, not even have I reached them in Multi Mission.
One more thing, if you get the chance to play this game then please use headphones of any kind to listen to its blissfully glorious soundtrack and sound-effects.