Mario 3D World and Mario Kart will help, but I don't think they will "save" the system from being anything more than the GameCube/N64 type console.
Wii Sports was the MAIN thing about the Wii. It defined motion gaming and inspired a hundred knock offs. That's why millions and millions and millions of people flooded in. Mario games just piggybacked off that success to monster numbers, but casuals won't buy a seperate console JUST for Mario and other Nintendo franchises. If that was the case, the Wii U should be doing at least OK as it already has a major Mario game on it already.
The tablet controller idea + Nintendo Land have failed utterly in generating any interest from the casual demographic, there's just no denying it.
Nintendo fans will buy a Wii U though, the price just needs to get lower and more games need to come out, but that's not what I think. That will get Nintendo a couple of years of so-so sales, enough to push it up to 20-30 mill userbase before the usual dreaded "last 2 years" Nintendo console curse kicks in.







