Bruges is probably the best preserved walkable city from the middle ages with great food & chocolates, we have toured. We agree with other folks comments. A must see in our view!!
Our Bruges was a post trip to Holland Springtime cruise, and had different optional tours (WWII Atlantic Wall & WWI Flanders Fields) & included tours (Ghent & Delft which were part of our base Holland cruise) than yours. However, your included tours, Ghent & Delft, are great & the Brussels optional is probably very good & one place we have not toured yet.
This Bruges extension sounds like it is a great complement to your Great Rivers main trip.