in the factory we use Wizards Mist and Shine for cleaning playfields, which is pretty similar to Novus1.
It is recommend to wipe down the playfield on a regular basis to remove any dust or grime. If you are not sure the last time you wiped down the game, it is overdue.
Changing balls can really vary from game to game, based on what the balls are hitting, e.g. how often is it hitting some kind of a metal edge. I recommend inspecting all balls each time your clean the game and replace if seeing any damage. Check for any scratches, dings, flat spots, etc. as well as making sure they aren not magnetized. When it doubt, replace them.