I think we need a new building that acts like the reserve but for items instead of pets. This way people who want to keep items from previous events don't need to waste warehouse space on unusable items.
Hello!
I believe that if you have unusable items in your "stash", then get rid of them, isn't it? If you wish more space, buy then more slots for it.
As well, it may be kind of unecessary to make new buildings after the fact you may just need the same money buying the upgrading as a new build.
There may also be another points to be noticed:
-How big or how many slots possess the "Museum"?
-It can be upgraded if it has a limit?
-It only can allow "event" or "rare" items or too any other item?
(If there should be only a event item, I believe the game itself must be re-compiled to add the new settings, with this I mean, create a group for items too!(if there's no one) ).
It may be kind of helpful to see more related information that allows all our community know better this fact. (:
Thank you for bringing up this idea, it certainly caught my attention.

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