People usually start asking questions about franchises needing a break when there's an obvious decline in quality. There is no such decline within the main Mario games. The last release is one of the highest rated games of the generation after all.
However, I would say that they could cut back on the spinoffs. Mario Kart and SSB should be more than enough, considering the longevity of each release in terms of playtime. Mario Sports games and Mario Party (and whatever else I'm forgetting) can be given a break for a while.
There is a difference between one character being used in a wide variety of games over various genres and a franchise seeing multiple spinoffs (and spinoffs of spinoffs) whilst mostly staying within the same genre though...
VGChartz
