Have you had chance to try the white Port they make in that area? I found it quite enjoyable and definitely different from the normal ruby red Ports. I've looked for it locally but so far no luck.
My wife does not drink, so I did not even visit any cellar while in Porto. I will keep an eye for what you describe while still in Portugal on this trip to see if I can have some to try.
Would it make any sense to rent a car, maybe in Lisbon, and do a loop of some sort? Rather then going all out with the car experience, just doing some short driving trips. Then using bus or train to get to other towns.
Also how is car navigation working for you? What GPS unit are you using? Phone or GPS to satellite?
There are several cruise boats plying the Douro from Porto to Regua in a long 12-hour day trip. This is possible because the water route is a lot shorter than the roads through the hilly region.
Much better than a day cruise is a one-way boat trip from Porto to Regua, then a night stay in Regua, then a one-way train trip back to Porto. Both the boat dock and the train station in Regua are just a few hundred feet from the main drag of Regua and the hotels.
From the center of town, a walk of perhaps 2 miles roundtrip along a riverwalk will take you across a footbridge to the south bank or the other side of the river, where I looked back at Regua and took one of the photos posted earlier. From the boat, you will not have the higher vantage points looking down on the river, but I am sure the trip is enjoyable and worthwhile.
My trip is auto-based, so I did not investigate the above possibilities until I saw several cruise boats docked in Regua. There were a couple of Viking boats, and they went up the river a few more kilometers to the smaller town of Pinhao, which I did not visit. Viking cruises are of course pricey.
About car navigation, I just used Google Map, which had improved a lot since my 6,000-km Europe auto trip in 2017. They did not have lane info then, which required me to have to switch to the outermost or the innermost lane to prepare for a right or left veer. This added a lot of work and stress on busy highways and streets.