Just as a general rule, I wouldn't worry about it until it starts acting funny.  They built NeX to be more durable, and according to longevity testing, SPECTO says it's pretty reliable . . but as with any other ball, just do what you need to do when you feel it needs to be done.  If you use surface, it'll just lane shine and go back to where it's at now.  Always follow the ball reaction, there's no mathematic or set schedule for any ball out there.  If it's fine, leave it alone, if it starts getting lazy/slow/flat, do something.