FWIW, I haven't learned the shortcuts on the maps yet. There are some cuts like in Mount Wario, and Rainbow Road that I'm not familiar with. I just learned about jumping the conveyor built near the finish line at Sunshine Airport.
Also, It never occurred to me to use boost mushrooms on the grassy areas to get ahead. For some reason I never did that until I saw everyone else doing it.
I'm pretty OCD about staying on the main road, which is why I HATE rainbow road because gravity seems to be my biggest enemy and I slide off all the time.