Venice: go out to the islands if you can. Can't remember how much a water taxi is, but Murano is so amazing. But even if you don't do that, make sure to get completely fucking lost in the city at least once. What an amazing place.

Is there a reason you're skipping Switzerland? How about the Jazz Fest? Pricy these days but I'm sure you can find an off-show. Is your wife into outdoorsy stuff? Go into the Alps. Most beautiful part of Europe. Find a hostel, get bikes, radiate outward. Message me if you want specifics.

In between Paris and Berlin is the lovely city Strasbourg, and south of Strasbourg are the Alsace Wine Route (for which you need a car, but if you drive stick rentals are cheap as shit in Germany, like really, like 20/night) on one side of the border and the Black Forest on the other. The wine is the best in the world and the food is a scintillating and unique mix of two cultures.

If you've never driven the Black Forest at midnight through the hills, unable to see the road in front of you ... just do it. Some awesome castles in the area too.