I can't tell if a diamond is worn using a 20X loupe. I was thinking of getting a 5 MP, 20-300X digital scope; but a totally gonzo cartridge/stylus photographer and re-builder on another forum posted that you need a combination of microscope and camera optics to get sufficient depth of field to see wear.
For $50 bucks, I may still try it if I get a new stylus for my MM. Then I'd compare old and new and see if I waited too long or long enough. Since the process is soooo gradual; I don't trust my aging ears.
I will say that I have a Shure V15RS with the original HE stylus from 20 years ago. I bought 2 new JICO styli, a SAS and an xMR. The HE and MR sound somewhat comparable, with the HE being stronger on the low end and the MR on the high end. Shape or wear??? I dunno; but I use the HE on older LPs with more surface noise. It is more forgiving and I figure the damage is done already.