I'd go with the Wite-out, or a Silver Sharpie, to replace the letters on the worn keys. (That replacement key link, and the nail pens, both look awfully pricey.)
I know we can't all go back to Junior High touch-typing class, or college freshman Keyboarding: "Ay, ay,ay, ay, Ess,es,es,es, De,de,de,de, Ef, ef, ef, ef --Jay, jay, jay, jay, Kay, kay, kay, kay, El, el, el, el, Semi, semi, semi, semi " so some of you need to "meet Mavis"! That is, pick up a copy of Mavis Beacon Teaches Typing. I think I had the 1st or second edition on a 5 & a half-inch floppy [who remembers those?], and the last time I saw it, was in the 15th edition. I bet there are other programs out there, too.
When I type, I use a cross between touch and hunt&peck methods. Sometimes I look, and it probably does make for slower typing. We can see the letters okay on both laptops here in my apt.,but on the other machine, the H and G key usually don't work, so I have to go back and re-type those letters--usually after I've hit "send"-- I think it's like using an old, Manual (non-electric) typewriter.