I thought Mario Kart and Hyrule Warriors were very well-priced for the amount of content provided, and I'd gladly jump in on similar deals in the future.
I wasn't a big fan of Smash Bros' DLC...but I am grateful they offered invidividual items rather than force me to buy a bundle of things I don't care for (Lucas, amiibo costumes, etc).
I didn't bother with most of the Fire Emblem Awakening DLC, despite me being a huge FE fan. It was all bonus material, and the few packs I played didn't really compel me to keep buying content. At the same time, since it was all supplemental material, I had no problem skipping it either.
I haven't played Fates yet, but I'm sure I'll end up buying every story-path. My stance will be based on how long the individual stories last, though what I've read so far leads me to believe they'll be on par with past handheld titles, so I have no reason to complain currently.
So far, my experience with Nintendo's foray into DLC has been positive. Like has said been said earlier though, this could easily change, but there's been enough positive examples for me to be optimistic.