I finally beat this game 100% today (all 242 stars)! I ended up dying exactly 300 times with Mario, and 151 with Luigi. Goes to show how much better you get the 2nd time around. Especially since I think the game is a little harder with Luigi, since he slides more and the races are MUCH more difficult!
What is the least amount of deaths that anyone got when completing all 120 stars with either character? Do you think anyone has ever gotten all 120 stars without dying? That would be one hell of a challenge!