Regarding amiibo cards, it's nice to know that there will be alternative methods to unlocking content associated with the figurines once the figurines are no longer available. Plus, maybe I'm interested in the functionality associated with a particular amiibo, but don't like the figurine itself -- allowing me to unlock that content without (hopefully) having to spend $15.
Case in point, when I tapped my Captain Falcon amiibo on my Gamepad today to unlock his racing suit in Mario Kart 8, I thought, "Man, it'd be cool to have the Fox and Samus suits as well," but I'm not interested in either of those figures. An even better example may be the Spinner item unlock in Hyrule Warriors that's associated with the Link amiibo, which is a figure I really don't think looks that good. I'd love to have that item, but not for $15. Amiibo cards could be a very nice solution to such things.