why keep them in box
New-in-box collector here.
Generally it's one of the following reasons that people collect in box:
1. They make a neat, organized display when they're in the packaging.
2. They're holding off on opening them until they have better functionality. Smash has the best use of the figures so far, and even then it isn't much.
3. They intend to sell them, whether it be soon or later on.
I'm case 2. I will jump ship and go out-of-box when/if Nintendo releases a Skylanders or Disney Infinity type game that uses amiibo functionality to its fullest.