Is Niš worth adding to a Serbia itinerary?
Niš can add depth beyond Belgrade and Vojvodina, especially if you are heading south or linking into the wider Balkans. On a short Serbia-only trip, it has to earn its travel time.
Answer
Niš is the kind of stop that makes more sense when the route is already leaning south. It adds Ottoman, Roman and modern Serbian layers that a Belgrade-and-Novi-Sad trip does not cover, and it can be a useful hinge if you are continuing deeper into the Balkans. But for a short Serbia-only visit, it is not automatically the next name to add. The question is what you would cut. If Niš replaces a rushed extra day in Belgrade or a thin Vojvodina detour, it may work. If it creates two hard travel days just to say you went south, the itinerary is probably forcing it.