The coin has been "tampered" from its original state, like trying to polish patina off an old fiat coin. I'd only offer face value, but that's just me!
there are a good number of casascius coins that have more then their face value loaded. A good number of them have been subject to spam transactions from various people, often of .0001 BTC or less.
The casascius tenth generally will fetch a premium of 1.9 or so when graded MS67 and loaded with .1 BTC. I would think that the premium would decline as more funds are loaded onto it. The premium would probably be the same if there is one or two spam/dust transactions and would only decline slightly if a small amount of extra funds was loaded onto it.
Lesbian cow was obviously able to get the coin with a smaller premium then what they normally fetch. I am not sure what this coin is worth, probably not 1.75 BTC in my opinion, however it is certainly worth more then it's face value, especially considering that it is a) graded, and b) received a MS67 grade.
Unfortunately the physical coin market is illiquid so it is not always easy to sell coins quickly and if coins are to be sold quickly they will often sell at a discount to what they would normally otherwise sell for.