Opinions vary, and are sometimes strongly held. However, evidence remains weak. No well designed research on this has been done that I know of. Perhaps somebody else can point us to a good quality experiment. Just because I haven't seen one doesn't mean a well controlled experiment doesn't exist.Some people love their cymbals to be highly polished and believe they lose highs if cymbals have patina. Some people are opposed to cymbal polishing and love the patina. They may also believe that this makes for a more mellow sonic profile. Or they may just like the look.Some people don't believe strongly one way or another. I'm usually a non cleaner although I've got cymbals which are old and crusty and some which look fairly new (because they were made in the last few years). I'm never a polisher. And I'm agnostic on the sonic effects of one road or the other.
Its hard to be sure whether the mellower sound of any particular vintage cymbal is due to earlier cymbal construction methods, the result of 40-60 years of playing, or the heavy patina that develops over time. It may be a combination of all three. Of course most collectors of vintage cymbals tend not to clean them in the same way that most collectors of antiques in general are not encouraged to perform any extensive cleaning. While no one can be certain of the impact to a specific cymbal if patina is removed, most people don't seem to want to take the risk of altering the sound of a great cymbal by removing it.