The overlay sheets and pen nibs are made to be replaceable. If you run your fingernail along the side, you can lift it up and remove it to replace it. The only difference that you'll see from the more worn areas is a different "feel" when the pen draws over it. It'll feel a bit more slippery, especially if you're using a second or third generation bamboo with the textured overlay sheet.
FruitTingles wrote:I use a bamboo with a very small active area. I have never used it for anything outside of osu! so naturally there would be areas (the active area and where I rest my hand) that would experience more wear. You can see this as it turns from matte (unused) to glossy (most used), will this affect the functionality of my tablet? I'm assuming your tablet is like that since you have used it for four years, but as mentioned works like new, so am I only wearing away at the aesthetic value?
The tablet's working bits are all on the inside, and have nothing to do with the contact of the pen on the tablet surface. If you place a piece of cardboard on the tablet and then start to draw, it will still work. The overlay sheet is just a piece of plastic, and so are the tablet nibs.
(My overlay sheet actually has gashes and holes in it... They're pretty expensive so I'm looking for a cheap material that has the same feel, though in the mean time the only difference I feel is the occasional small bump when the pen runs over a scratch or holel. Protip for the pen nibs, you can use plastic wire from a weed whacker that's the same diameter of the nib for a cheap, effective replacement.)