Like most Pokmon cards, the value of Spiritomb depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Steam Siege)
MTG cards are the standard trading card size
It's been reprinted in a Masters set, a Secret Lair, and even served as one of the Grand Prix promos for a year, and never has it been anything more than just alright
It's hardly a shock to anyone paying attention to Pokmon TCG that these price hikes are occurring, especially with such fervor from fans to find these particular cards in the set, which is why many investors are treating the Scarlet & Violet 151 Booster Bundle as a "legacy asset": a "piece of history" that is more valuable stored as is rather than opening packs looking for a rare card that may get lost or, as we used to do back in the day, traded to a poor kid who has no idea that their Charizard card was, in fact, far superior to a lousy Caterpie card
Choose one to keep