Hi FurryFrog, Well for the 1968 the front is very dull with a greenish tint and the back is very shinny. As for the 1988, the E and S in the word states on the back side are not there and there is some discoloration in the same area.
In my defense, I've had a few beers tonight. Nothing like being on leave, drinking some beers, and looking at coins
The 68 is just dirty. The 88 is what's known as a grease filled die. Basically, some gunk got in the die when the coins were minted. If you look through a lot of cents you will see that this is a fairly common location for this to happen. No premium over F/V IMO. Keep searching