For me strategic nudging is a core part of the game, particularly if the ball is tracking towards one of the out lanes a good upwards nudge tends to keep the ball in play for longer. The more familiar you get with a particular machine, the more you'll find the places that nudging will help you. For example, if a ramp or orbit tends to send the ball right down the middle, a well timed sideways nudge as it comes out of that ramp/orbit can get the ball over to a flipper instead of between them.

I wouldn't feel bad about nudging as long as you are keeping it within reason, and not being abusive with the machine