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I think it's worth it if you've got an original 3DS. It's probably what you'd get selling it through eBay minus sellers fees etc.

For a PS Vita or 3DS XL...hmm. With the former, I guess trade in programmes like this are a hassle free way to switch platforms, even if you are accepting slightly less for the device. I personally made the jump from an original 3DS XL to a new 3DS XL (wanted the Majoras Mask edition), and from a technical perspective it wasn't anything revolutionary.
 
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