Just to add to what everyone is already saying, I would also be sad if we could no longer have duplicates in galleries.
I have an in-progress gallery of all things 'chai' on the site (the pet, any item with 'chai' in the name, etc.) and many of my friends will send me little things they've picked up that belong in my gallery. It makes me happy that they were thinking about me when they saw a particular item, and I like to add it to my gallery regardless of whether or not I already had it. If there's 26 of an item in my gallery, it's most likely because my friends sent them to me, and I definitely want to show off how amazing my friends are. u_u

I collect zombie kitten, zombie kitten plushie, and squishy zombie kitten plushie as well as the red and blue alien plushies and birds/bird related things. I have multiples of a bunch of them and why shouldn't I? Over on Neopets I collect Petrified Bone and I have a bunch of those over there. I like being able to collect as much as I want.
Putting up more and more limitations is just going to make a bunch of people mad. We can, and more than likely will, leave. Either that or severely limit our time here. If multiple items were causing issues then staff would've mentioned it before, from my understanding they aren't an issue.

Hampton the Hamster, my pet, currently has 32 in his TC. Does that mean I should have a limit for that? No. In fact, he'll be getting even more in a little while.

No, you shouldn't have a limit for your treasure chest, because each unique item goes in a separate spot, so you still have to have 32 unique slots to put 32 of the same item.
There is literally ZERO reason for anyone to need to have more than one of a unique item in their gallery. These are pixels. 64px x 64px images.
I just want to reiterate that having multiples in your gallery has no additional effect on the servers to having one of an item.
So really there's no good reason to limit that.
I have 100 because I WANT 100 . That has no effect on you as a person whatsoever.