Shimming is usually not necessary on account of cam wear but more because the seating of the valves and valve wear. When I adjusted my clearance there was no noticeable wear on the shims or lobes, but in in some cases the clearance was .005" out of tolerance.when I checked the valve clearances on my bike at 12,000 miles, found it was not necessary to re-shim.
the clearances were in the middle tolerance.
I was amazed that the cam lobes had hardly any scuffing marks etc and looked brand new. its not like that I treat my bike with kid gloves either and only change the oil at 6000 miles