The cleaning issue get's a lot of discussion in coins, but I like the term harsh cleaning better. In general I do not view the removal of foreign material on a coin as harsh cleaning as long as it does not alter the metal, regardless of what condition the metal is in. If the cleaning method removes metal than it's harsh cleaning. So dirt in the devices, lacquer added by a previous owner, milkshake residue , all acceptable. Removing those black carbon spots or smoothing corrosion would not be OK.
With that said, I have seen coins which have had rim dents 'improved' and honestly I think it increased the eye appeal, and value, of the coin. I also have cleaned coins which have been intentionally recolored and again it was for the better. I would pay more for a problem free coin which did not need improvement in both situations, but I would also pay more in both of those situations for the improved coin than for the unimproved coin.