I can't touch-type, and my hunt&peck is very "poundy". So my keys wear out fast. I had about a dozen that were impossible to read anymore. Well, maybe I can't touch-type, but I do basically know where each letter is.
But out of curiousity, I went looking for replacement keys. A bit expensive. But what I also found were press-on decals.
They seem to be very good. The print matches most black keyboards (there might be white/cream/gray decals too), the vinyl backing is sturdy, and they seem to stick well. I got mine at Amazon ($6), and there are 2 full sets of key decals.
It looks like a new keyboard!