I'm surprised you have that takeaway for NFC since you have played some rhythm games at least. For the most part I'd say on most rhythm games I've played (IIDX, SDVX, Groove Coaster) it's pretty much storing your song scores so you can see what you've played before and you can go to another arcade and have the same data there too. I feel it's less of a grinding thing and more of a player convenience there.

An interesting thing is that you don't have to buy their NFC card either, most of the Konami cabs (e-amusement) can accept a Suica/any IC transit card (a side effect of their card systems both using FeliCa).