I have not heard of paint wearing off to bare metal on a Thorn before.
My Nomad Mk II and Sherpa, if I recall correctly they used the base paint (or maybe it was a powder coat?), then added the decals, and a clear coat on top of that. The clear coat protected the decals. In some places, the clear coat flaked off of my Nomad frame, but since it was clear it is not something that is easily noticeable where it flaked off. Clear coat on my Sherpa did a great job of protecting it.
I had a Surly years ago, that had a soft powder coat that easily wore off. I bought some fingernail polish that was the closest match to it that I could find and used that to touch it up. Maybe you could do the same?
If you found some fingernail polish to apply to the places where it is worn off, that polish may be more durable than the original paint, you might only have to do it once. I use black fingernail polish on my racks for touring where the racks were worn down to bare steel, the fingernail polish is pretty durable. Fingernail polish is very convenient, has the built in brush, etc.
You can buy a clear coat version of fingernail polish. If the paint on sharp edges wears off easily, you could apply some of that on the sharp edges to protect it.
Bicycles are supposed to collect nicks and scrapes and dents over time, I suggest you don't replace the fork. The only reason I touched it up on my Surly was that I hung the bike on a car rack and drove a couple thousand miles. Where the rack and bike contacted each other, the powdercoat wore off, that was just tooooo ugly to live with, thus I wanted to try to restore that.