Shrug. I just buy new $10 on-sale "gaming" mouse pad, from Kingston, Corsair, Patriot, etc., some gaming company that sells small-med cloth pads for gaming optical mice without charging an arm and a leg (over $10 for small, or over $20 for med-large).
I also peruse Newegg fairly often, and if I spot one on sale, I grab two or three.
Not that I don't advocate cleaning off your mouse pad when it gets dirty, I do that too. I run it under water, apply a little dish soap (Dawn?), and wash and then rinse it for a while, then put it as flat as I can, into the drying rack, and leave it for a day or two.
I just mean, replace it when it gets REALLY frayed or crufty.