My city recently got districts included as nested cities (thanks @JamesChevalier !) and my number of cities almost doubled 
I think it would be nice if there was a way to easily distinguish nested cities. Maybe a lighter shade of purple for progress bars and other buttons? The same pattern could be applied for streets in the activity view, where the “show” and “go” buttons could use the colours.
In the activity view it would be cool if there was something like a selector in the completed and progressed tabs to choose which streets are shown (“parent”, “nested” or both). It’s great to have the full breakdown available, but my guess is that most striders are working on one of the two levels and having streets shown at both levels makes the lists a bit unwieldy.