there are a few games, ones of old series that didn't sell well, thouse will go up like crazy.
before XC got the n3ds version, the price for that was sky high, and remained quite high untill future connected was announced.
Fire emblem radient dawn, sold less then its NGC predecessor, goes for higher prices then PoR.
but the limited amount of actually good games that didn't sell like crazy means... well... these are outliers. there are vastly more copies of galaxy roaming around vs sunshine, even considering sunshine sold half: nearly all people who bought sunshine are now pretty hardcore nintendo gamers(ergo they won't sell it). meanwhile galaxy was bought by most everyone.