As a coin collector, I would never clean a coin. The cleaned coin will have an artificial appearance. Metal coin surfaces show wear quickly and it is very difficult to remove dirt without negatively effecting appearance.

Chips tend to wear more slowly than coins. A chip that is slightly used, new except for a little dirt, can usually be cleaned without creating an artificial appearance. Worn chips when cleaned will not look new, but some worn chips look really ugly and with a gentle cleaning can have their appearance improved.

It's a matter of common sense and individual taste. I like to have nice looking chips.