Yeah, I definitely get that by opening the chests you have the chance to then find the better cards that you've unlocked, the wording in the store page makes it almost seem like there's a buff of some sort, like an item find bonus in other games that gives you more likelyhood to find more rare items depending on how many treasure chests you had. Like it would change the loot table when the location decks are built to add better cards, rather than just being fully random with all available cards.
If having unopened chests gives you better loot chance, that makes me want to horde a few, otherwise I'll just open them all up.