Wanted to post this since it is much discussed and most experts routinely recommend against it.
While I cannot comment about any towns further than Rio Maggiore or Manarola I wanted just to post to say based on my experience any fears are much overblown.
The drive could not be easier and any GPS or app will route you the best way. The worse part of the drive is the slow grind of driving through the not very scenic town/city of La Spieza. The winding mountain roads after La Spieza were pretty and very simple to drive, never scary or very curvy compared to other parts of the country.
The views were very nice of the La Spieza harbor from high above and we would have missed that on the train, timing is roughly the same but happy we did not have to fight with our bags with the crowds in a train station.
Parking in the main Manarola lot for our 3 night stay was cheaper than parking under the La Spieza train station and our car felt very safe. They offer a discounted rate for staying more than 1 night.
Depending on where you are staying the walk from the car parking lot may be better or may be worse than from the town's train station, at least in Manarola they are in opposite ends of town.
Just my $.02