I agree with the Prof. Large cents often look best with the dry brushing especially if you have some dirt/clay still on surface than lightly apply some nose grease to top surface of the coin letters and pattern. This brings out some contrast.
If the shield nickel is not a valuable year, you could try a concoction of hydrogen peroxide and white vinegar, short baths and a scotch brite pad. It will turn the nickel silvery and bring out details, but it will kill any value if you ever plan on selling.