I have some EPSN trays that are badly worn...just form using. I sure wouldn't use anything abrasive on them...if I could help it...guaranteed to wear down the silver. And because it's nickle silver under you won't see it right away.
There is something on the market that actually lays down a thin coating of silver when you polish. It's meant for polishing plate with worn spots. Don't remember the name of it....and it is expensive....but it would solve your problem.
I'll do a search....see if I can come up with the name of the product.

It's called Liquid Silver....and the reviews are not terrific...but I have a friend who was a silver collector and he swore by it for his stuff.

Thanks--I'll look into it.