It used to be that a polished old K was as bad as a rewrapped drum, but those days seem to be over...I don't think polishing old cymbals is as big of a "no-no" as it was in the past. I've seen polished old K's sell for extremely high money, and I've seen heavily patina'd old K's fizzle out on ebay.
In terms of sound, in my experience a cleaned cymbal is more "alive" - more bright overtones, washier, louder, longer decay. Elvin always cleaned his cymbals, and he usually played in environments where he could be quite loud and bombastic (he constantly cracked his cymbals).
An old K with a lot of patina is darker, more dry, shorter decay...this appeals to the jazz guys that are going for a dry tone, especially in bop type music where there is a lot going on, and you want the tone to speak quickly and get out of the way. This goes hand-in-hand with Gretsch RB drums...they are dry, the tone speaks quickly, and they get out of the way. Great for a jazz trio gig in a small, subdued and low volume environment.
I notice when people come over to try old K's or A's, drummers that prefer cleaned/polished cymbals generally start playing them loud right away, like DING DINGA DING DINGA DING!!!! Guys that prefer the patina generally start playing them quite softly right off the bat, like they've used to playing in controlled situations such as a restaurant. Not always true, but enough for me to notice.
Thanks,
Bill