I don't know about the newer ones but i assume they are basically same as the old. I have had the same qpad for about 8 years now and all it needs is a bit of washing. I just rub it with a sponge under running water, let it dry and then after some playing it feels fast again. If you want to test your shit level on your qpad, then just make your finger wet and rub the pad. The amount of shit that usually gathers there is astonishing . At first it does feel really rough but it goes away. Some say that you can iron it for it to become smooth again but haven't tested it myself - I prefer 'playing it out'.
My QPAD Gate 01 is 4 years old. Not really dirty, I tried it - and my 7 years old Allsop Raindrop is faster, so as my 4 years old Razer Mantis Speed. : /