I am actually engaging with My Nintendo extensively, and doing some serious budgeting to make sure I can get things I want.
However, MyNintendo is DEFINITELY lacking a Wow factor for a highly-engaged fan such as myself. I think maybe that boils down to a lack of real exclusives (Miitomo clothes not withstanding). The easiest way to satisfy that "cool item I must get" desire is with neat physical gear ala Club Nintendo, but that's an inventory risk for Nintendo. Still, it would be excellent for some level of physical rewards to return to Club Nintendo, even if it was just for 800 gold coin hanafuda cards.
Another way they could resolve the need for wow is more digital exclusives, ala Twilight Princess Picross. It's a small and super budget game, but the exclusivity, IP, and pure simple joy of picross means I'd rebuy a reskin (Pikmin Picross?) every 6 months happily.
Alternatively they could make my dreams come true and unveil an entire lineup of rewards where I redeem platinum or gold coins for Mii outfits in Smash Bros.