I tend to put this in the same camp as whether or not to tee it up when allowed, if they let you clean your ball before you tee off and when you mark on the green, why wouldn't you? Even if the difference is minimal why leave it up to chance.
I've always approached it the exact same way. I always wipe it down on the green after I've marked, and I'll give it a quick wipe on the way to the next tee. I'm always using the ball washers as well.