Positano is beautiful. I will say that on our two visits there, we had a very short time there (it's never long enough in Positano), as we had to fit in the other stops in busy traffic. The drive is a while but I honestly don't remember it being long. There is so much to see along the way - it's a very scenic drive. The driver (while not a tour guide) provided a lot of great information along the way, and made a few photo stops along the road. I didn't get car sick, but asked to sit in the front of the van and I was fine. (One in my travel group took something and promptly fell asleep, and missed a lot. 😄).
Yes! It was worth it to me. The beauty of taking a tour like this, is that the driver can make changes to the itinerary, and stop if there is a need to with a small group. They will also take you to a restaurant for lunch somewhere along the way, often with a wonderful view to enjoy.
In my experience, after posting on my roll calls, here and other places (along with having Jany add it onto their website that my tour was open to share) it can take a while for others to join. We filled our van days before our cruise the last time I travelled. Some wait until just before they travel to look at tours. My small group of 3 decided that even if no one joined our tour, we were ok to pay the tour rate, because we wanted to visit
I would suggest to go with what you feel you're the most comfortable with. 🙂