Ninja Spirit is a special case, because they made a lot of copies, knowing it would be popular and it is one of the few games to ever get a 10 from EGM. But it was also a case-less pack-in with the TurboDuo.
Colletards and gougers will try to twist this around to claim that the case is super rare and valuable. But it was a very common game CIC and CIB and the loose game is only that much more common and unvaluable.