Are Troy and Nancy worth a visit each?

Nancy is worth a multi day visit . This is the heart of French Art Nouveau in Architecture , Fine and Decorative Arts . The center of the city is the Place Stanislas ringed by the Art Museum and the Opera house . I spent close to a week there a few years ago , and it was well worth the time The TI in town has an excellent map highlighting all the important sites , easily reached on foot or by bus and tram https://en.wikipedia.org/wiki/Nancy,_France.

If you are motorised, then I would recommend going to Troyes not only to explore Troyes itself but a bit further east, which can be done much easier with the car than by public transport. Going to Troyes by train is direct from Gare de l'Est. The rental car will take you out to that little place, Brienne, if you're interested in Napoleonic history. The expanded museum is in Brienne, appropriately so since he was sent to military school there. That very building is now the expanded museum dedicated to Napoleon.

Aside from that Brienne is the site where the invading Allies , this time the Prussians and Russians, first encountered Napoleon on French soil. They lost.

Troyes is also associated with Napoleonic history as is Fontainebleau, obviously. If that is not in your interest area, then I suggest going on to Nancy.

Troyes is really worth it! Very well-preserved medieval town center, and champagne as a bonus.
I am not a fan of Nancy BUT I do not care for Art Nouveau (I like clean lines), and that's one of the main draws there.
Verdun is another option, roughly on the way. Can't advise on the specifics of a visit there.

Really liked both cities. I didn't notice many other tourists in Nancy at all, and those I saw in Troyes all seemed to be French. I'd happily go back to both places. I think if you have a special interest in Art Nouveau architecture, priority should go to Nancy.