Well here it is. I got the Zelda one obviously, not the Animal Crossing one. It came in an unpadded shipping bag with the little Toad card you see below which is just blank white on the back. All three interchangeable cover art inserts came inserted in the case (3DS Art on the outside, Mario in the middle, and Zelda on the inside), and the case was sealed with a cheap "resealable" polybag (the adhesive was stronger than the plastic so mine ripped trying to get it open
).
Pretty sturdy little case and definitely has functional value. Looks like as of now the Zelda one is sold out on Club Nintendo but you can still buy the Animal Crossing one. These have sold on eBay from $8.50 for a broken one all the way up to $29.00, so your prediction was spot on, Knight.
While searching eBay for this, another card case set kept popping up in my results. I thought maybe it was Japanese or European at first, but no, this one is North American too. Released in February 2012, and yes it has Zelda. Damn, no idea how I missed this. It's selling for the same and a little more than the one we've been discussing here.
A little research shows it only cost 250 coins at the time AND it came with 4 cover art inserts instead of 3. Go figure. I'm thinking you made the right choice holding your coins Knight!
Edit: Oh yeah and since we were talking about it here I got the other Majora's Mask OST I was expecting so PM me if you want a rip.