so.. How long is too long, and how long is not long enough?
That's for you to decide. I don't even tumble brass out of my bolt actions because they just don't get that dirty, but out of my suppressed AR's, if I don't tumble them I'll never have a chance in finding the dirty SOB's on the ground.
I've never found shiny brass to shoot any better than brass that's a little dull.