You could try a Hydrogen Peroxide bath to get more detail, but some of the guys on here might caution against it. If you want to keep it for yourself, go ahead and try the HP bath, it will definitely help bring out the detail. At least on mine, it's helped a lot. If you want to sell it, might want to wait on the bath.
I used the 3% stuff you get at Walgreens in a brown bottle, put it in a microwave safe cup (like a coffee cup, but make sure you don't accidentally drink it), heat it for 30 sec and then pour it into another bowl and drop the coin in. After it stops bubbling, you can use a toothpick or a light brush and a bunch of stuff should come off. Go very slowly though so you don't scratch it...
Good luck!