Flywheel worn? This is the first time I have heard of this. Is this common in the UK?
My mate, the boy racer in the far east, would even lighten the flywheel for performance but not good if you are going uphill though with lighten flywheel.
You don't wear through them, just wear away at the surface. If the surface is rough then it needs skimming smooth again, otherwise you'd just wear out the next clutch.
Lightening is a different process, you could take away material from the perimiter, the thickness, the center, wherever, or just fit one from a smaller similar engine, all it does is improve acceleration at the expense of making the engine a a bit lumpier and harder to pull away without stalling.