9,999,999 points
When the "GENKI" logo screen appears, hold Start + L1 + L2 + R1 + Down on controller two. Then when the title screen appears, release the buttons. Now start a one player game, and the game will display 9,999,999 points.
Quick lap
Just before a race begins, press Right. Then when the race starts, tap the acceleration button to turn 90 degrees. Now the game will record the first lap as finished in less than 3 seconds.