IWC's service costs are pre-determined, so a complete service for a Valjoux-based movement is already known and takes into account various parts that may be worn and need to be replaced. Therefore, I would not expect, nor have I experienced, any extra charges for parts replacement due to wear. Also, the Valjoux 7750, which it is based on, is so commonplace, replacement parts are easily accessible and inexpensive. Besides, the 7750 is tried and true workhorse that can handle a little wear.
What I am more concerned with is keeping the dial and hands original and the case in unpolished and unmolested condition. There is no telling what damage an undertrained/inexperienced watchmaker might do. And if you do send it to IWC for service, certain parts may be required to be replaced in order for warrantied service to be performed. If there is any chance that the tritium lume on the dial or hands have started to degrade, the dial and hands will have to be replaced with more modern versions that have Luminova instead of tritium. The hands and dial will no longer be original, will look different, and will affect the value of an otherwise mint conditon, very collectible piece.
Like Tilo said, if it ain't broke, don't fix it.