I would give them a bit of a wash, even if you do not polish them; a gentle wash will not remove any patina that might have developed. A patina can be nice, but there isn't anything attractive about dirt. I don't think the crests were intended to be worn in that condition, and I don't think it honors the entire concept of a clan crest to wear with an accumulation of old grime. Cleaning them would also protect the original finish and prevent corrosion in the future.