I personally don't like dirt and I clean just about all of my chips that would look better cleaned, but it's a personal choice. I firmly believe, however, that if you're selling a chip, clean will almost always fetch more money that dirty, unless the chip is very worn.

I will tell you this... you shouldn't worry about the hotstamp on this one. The older hotstamps will stay intact no matter what - you can even use a dentist's tool on the hotstamp to scrape dirt out.

The newer hotstamps are a lot more fragile, and I usually use my thumb to cover the hotstamp while using the same procedure and materials that Steve uses above. I would not, however, clean just the outside of the chip and leave dirt in the center of the chip where the hotstamp is... that doesn't look right.

Be VERY careful, though, with most of the Christy and Jones hotstamps. Even if you decide to cover the hotstamp with your thumb, I can guarantee you that you will lose a lot of the stamp. Unfortunately, I learned this from experience with a rather pricey chip, but if you think about it, you do see some Christy's with virtually no wear that are missing most or all of their hotstamp... so I recommend that you never clean Christy's.