I've seen very many people on VGChartz say that the Mario series "Is so milked it's not even funny" or, "Nintendo just doesn't know what to do other than milk a series not even worth the cost of a cardboard box." And I say to these people, are you crazy? Mario is the best selling series out there. You just can't beat it, and, obviously, Nintendo can't either.
If people are still enjoying the series, what's wrong with a bi-/yearly release? Nothing, I tell you, nothing.
You can start whining about "Mario is so milked!" once Nintendo start releasing more than one in the time span of a few (like 3 or so) months.