I can only reply with my experience over here. It doesn't cost you anything to apply, you have to have a certain amount of Nikon gear which you probably already have and you need to show you are a working pro.
The advantages are small but worthwile imo. I get priority with repairs and if necessary loan equipment. This is what I mainly use it for. An example, my D800 felt terrible colorwise, the too green issue. The repair center had it calibrated in every way the new possible including a focus adjustment ( which I did not even ask for) within a day and had it returned within a couple of days. They could not see anything wrong with it but since I vented it did not feel good they were willing to do all the work just to see if it would make a difference to me (it is now a lot better in my eyes, apparently I am very sensitive to green or something).
Other people use the ability to loan equipment during events, check and clean every 6 months (I should be taking advantage of that). seminars and trainings are arranged as well, either for free or heavily discounted.
I had the impression in the US you can have priority buying new equipment, not sure if that applies over here too.
NPS, do you really need it? Maybe not but it sure feels like Nikon will take care of you when you need it. For me that makes it valuable.