I dont think the frame rate will be increased. It will probably just be fixed at 30 or something. Its really not that jaggie, considering it will be 10times harder to notice them while youre playing. It can only be the same or better in the graphics department so i dont think you have much to worry about.
Im hoping that those slopes are downhill drift courses. That would be nice. The level of customization seems to be increased and thats always good. The first game was too short for me. After i beat it, i saw no reason to continue, considering i dont have the network adaptor.
It would be kinda funny if you had shitty ass sound untill you upgraded your stereo. Gives you more of a reason to win/customize etc.