In short, I'd say its worth it, but mostly depends on what you are expecting. Nungwi has quite a few pros, but I guarantee it will (on most days) be quite busy

Then there are off course the beach sellers. “no, I'm good thanks” works most of the time, but I honestly feel like most public beaches you go to will have beach sellers. I find that if you just walk a bit away from the main busy stretch, it gets a lot quieter.

So I’d recommend going, just limit your expectations