Prevention is better than cure.
If your 7750 runs smoothly, winds cleanly, sets accurately, etc. then there's probably no pressing need to get it serviced, but you should still consider it. If it feels gritty or doesn't run as smoothly as you'd like, get it serviced as soon as possible.
If you wait for problems, you'll be paying for parts and service instead of just a service. You can't un-wear metal.
Still, having said all that, if you paid $250 for a cool a7750 watch, there's no point in getting it serviced if you'd prefer to replace it for $250 than repair it for $200.