I have multiple pads, along with multiple backs. I use one for each product. To clean them, I get them wet, spin them in a bucket at the highest speed to remove excess water, use a toothbrush as needed for heavy caking, then pad side up, on the ground I press firmly with a towel going slowly from the center out as I spin them clean and moist.
I too, have pads that are 5+ years old, done more cars than I wish to count with, and still in beautiful shape. If the pad gets a little warn I also give them a light re-shaping with a 2" square brass brush... kinda like turning a brake rotor on a lathe.