I don't know, I mean, I feel like Mario's voice is getting higher (in pitch) in new games (except Smash Bros.), specially in 3D World. I still can't believe Mario is ~25 years.
I'd be ok with an actual WarioWare (I'm still waiting for a microgame based on Rhythm Heaven). Game and Wario feels very poor in comparison with earlier WW games (though I like the drawing game).
I doubt it has lost its charm. I mean, Mario Kart 8 and SMM were a big success. But I do think that they have to improve some spin-off games. I'd love to see another Strikers game, but instead we got a incredibly basic Mario Tennis game (in terms of modes, characters, etc.)