"Power is nothing without control" really seems to apply to the dirt and snow races, which is why I think you are best off using a stock rally car--I like the Subaru Impreza--rather than adding a turbo or going for a fully-modded 4WD street car. The big turbos provide poor low-end acceleration, and the car can become difficult to control at higher speeds, making it easy for those 5 sec penalties to pile up. A stock rally car, on the other hand, has a better balance and driveability. That's how I was able to win the Yosemite I (Hard) races at 58 points in a regular Subaru rally car, after I lost the race at 1 point by over 20 seconds in my +700 bhp Skyline.
Of course, anticipating the turns and breaking early is also essential, because no car is going to drive well if you are constantly hanging sideways or hitting things. Speaking of which, if you are about to hit something or are riding the walls, make sure to turn in early and kick out the rear a bit, because hitting the wall with that part of the car will not penalize you.