It would be so cool if you had a RPM meter up above the health meter, and you had to switch gears when you hit a certain point. It would be good because good drivers would know when to switch and would have good accuracy, while bad drivers would be slow and not accelerate very fast.
I think that going down speeds that you shouldn't have to switch, because the space bar is the only good button to use while your driving.
Also, if your RPM is to high and you don't change it , it should cause damage to your car.