The value need not necessarily be lowered. When the new owner transfers coins, they could be required (checked by the chip) to add an input of theirs to the transaction to cover fees. So the value of the coin stored inside the device will always be the same.
Good idea. While this would make the device handling a little bit more complicated it could still be simpler than with today's hardware wallets if it's implemented in a smart way. You could, for example, combine it with an (obviously open source) app for mobile devices which can not only check the addresses connecting to the blockchain, but also always automatically add the required input for the fees - ideally for several of these "coin devices" at once.
The big question is, however, if this kind of device would have a market - specially, if people would see an advantage in a device that has always the same value, compared to a standard hardware wallet. Because simplified hardware wallets with variable amounts (kind of "Bitcoin smart cards") would be probably nearly as cheap to be produced. I think these "smart cards" (which basically could replace credit/debit cards) would make overall more sense.
