Collectables require climate control, no exceptions
Toys can be collectables, but collectables are never toys, does that make sense at all? Anything that has real value can be a collectable, be it a book, a comic, a toy, a game, or a glass from when McDonalds gave away things made of glass (probably before your time).
But if you buy an action figure, for example, and then remove it from the package to play with it like a toy, then it is no longer a collectable.
Collectable items sold on the secondhand market need to be mint condition, still in the original packaging, and never having been played with. To help keep them in the best condition I recommend using a dedicated HVAC system for your collection. Of course you need to have a private area, a sealed room for example, and it should have its own climate control system in place. In the worst case scenario you can use the central HVAC system for your house, but even then I think you need an additional dehumidifier for the collection room to get rid of that extra moisture. Nothing ruins a collectable — any kind of collectable — more than moisture, so a dehumidifier is worth its weight in gold to a serious collector. Of course if they are out of the packaging it doesn’t matter if they get moisture damage, so whatever, but if they are in the box then don’t scrimp on the dehumidifier. I was lucky enough to build a collection room in my basement, where the walls provide temperature moderation I just need to use a dehumidifier not an HVAC system.