Zildjian A's and K's (non brilliants) don't suffer if you clean them. I've owned my current set for almost 20 years and have cleaned them several times and I do notice that after getting rid of years of dirt, grime, human acids, etc.,...after a good cleaning they sound shimmer-y and pristine and less gong-y.
I use a product called "Groove Juice" which is a lemon citrus-based product, and all you do is spray it on pretty liberally, wait a few seconds, use a sponge to kinda' scrub it a bit, and then rinse it off. Then flip it over and do it again. I usually do this on a table out in my backyard. The plates come out with a new shine and in most cases, completely clean.
I used to subscribe to the 'don't clean them' approach but I think as a cymbal gets dirtier, it gave me the impression that the cymbal is coming to the end of its life span, and this is definitely not true. Not having any money to buy new cymbals, I thought I'd try cleaning them, but of course, didn't want to work so hard. When my drum shop recommend the Groove Juice stuff, problem was solved! New-sounding cymbals with almost no work!