You are correct, this is a much different experience than some other European rivers. The river-side villages and towns do not compare with those on the Danube, Rhein or Moselle at all and your wife may be disappointed. There can be morning and afternoon excursions in the same day depending on cruising time and overnights. The ship may also move while there are shore excursions, usually by bus. Expect a fair number of bus trips and a fair amount of free-time. The nightlife is really only in Porto but most of the better cruise lines will have an evening event with dinner at a winery quinta. You should expect multiple demonstrations and performances on your ship during some of the sail times and in the evening. The scenery is beautiful and very dramatic in some places but in general the cruises can be very slow-paced because of the daytime sailing.
I’ve sailed on der Rhein, Moselle, Danube, Mein Canal, Rhône, Sâone, Garonne, Gironde, Dordogne and Seine along with numerous French Canals and I would say the Douro river was my least favorite but I really like the country of Portugal.