Rhine and Mosel Suggestions
Everywhere you go is going to be excellent as far as wine. Krov is one of my favorite little towns, they have a summer winefest and international dance show, but I think you will be too late for that.
Mainz is another good city to try. The Kupferberg Sekt factory is there and they do guided tours with tastings. They also sell bottles that aren't available for sale anywhere else, just at the factory.
Bern Kasel is a wonderful spot. Bern Kasel (castle) is in the region of Mosel and the wine country. There is wonderful shopping and the hotel has a wonderful restaurant. You can hike up to the Kasel and it is not too taxing and the castle is wonderful to see! Also keep in mind that each region or county has it's own beer. In Bavaria which will not be on your trip but is considered Munich or Munchen is Bavarian beer which most peeps have heard of ....the Rhein and Mosel (depending where along the Rhein you are) is typically considered Kolsch beer and it is really good. Not too strong....more of a lighter beer. Kolshch is from the region of Koln or Cologne. Ask your driver or the hotel if you fly into Dusseldorf! Hope this helps!