Welcome to the Vintage Forum. That looks like a nice diver's watch from probably the 1960s or 1970s. Nivada (located in Grenchen) used mainly ETA movements. Once it has been serviced and the crystal has been polished, it should look rather good.
Whether it's worth servicing such watches (decent but generic movements) always depends on whether you will wear it. It is practically never worth it from the purely financial point of view, i.e. if you want to sell it afterwards (the costs of the service will exceed the added value). However, it is almost always worth it (at least on a functional watch needing no parts replacement) if you want a watch to wear since the cost of the service plus what you will (or should!) have invested in buying the watch will be less than the cost of a new mechanical watch of approximately the same grade (with modern ETA calibre) and the service will greatly increase the watch's longevity and make it run rather more accurately. If it will just sit in the drawer after the service, it is obviously not worth the investment since even unworn, the lubricating oils dry up so that ten years later, you will need to have it serviced again anyway.
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