I'm not going to get into the debate over the quality of NSMBWiiU vs. SM64, but I will say this - for all the top-tier, high quality, groundbreaking frst-party titles the N64 had, it was still crushed by the competition in sales.
Meanwhile, for all the nay-saying against the Wii U, it's not too far behind the XBox One and only about half of the PS4 (yes, half isn't good, but compare N64 to PS1). And I'd say there hasn't really been an amazing, revolutionary, ground-breakng Wii U release yet.
I think folks overestimate the impact of a "System Seller". If I'm buying a $99 Game Boy, sure, Pokemon might do it. But when we're talking about dropping a couple of Franklins... I just don't see a sizable amount of people doing that.
People buy systems based on one of three things:
A.) A fan of the manufacturer/their promises of future supprort
-Nintendo has pretty much tapped this group out.
B) My friends have it and I want to be cool/play against them online.
-Never going to get the first group and they really don't appear interested in the second.
C) Man, this system has a bunch of games I want that I can't play on the system(s) I already have and it's a good price.
-This is the group they need to cater to now. As was pointed out above, they've done a lot of damage putting out comparable titles on the 3DS (although Smash 3DS isn't in the same league as Smash U. Mario Kart 7 plays better, imho, but 8 is getting amazing DLC)... but this is how they fix it. One or two completely mind-blowing AAA titles isn't going to reverse their fortunes (aside from Pokemon MMO, but we already discussed that Nintendo isn't catering to an online demo). They just need as many good-to-great AA-A titles as they can get.
With that said, they need to crank out more games like Hyrule Warriors, Captain Toad, etc. They need to figure out WTF is going on with the virtual console (get every first-party NES, SNES, N64, GameCube, GB, GBC, GBA, and DS title on there tomorrow. What, we can download Wii games? Whoopte-f***in-doo. I can pop the disc in and play it. Hell, I can go buy a used Wii for $30, the game for $20, it's cheaper than buying a Wii U and I have more choices in VC titles...). They need to get with third parties and get as many of their classic titles on the system as they can. Not that I see SE getting on board, but could you imagine if they announced tomorrow that all of SE's SNES titles were coming to the Wii U? There are folks that would buy a Wii U within hours of that announcement.
Face it, Wii U isn't going to get new third party support. So, throw all the old stuff at it (F-Zero GX, AX, F-Zero X, and F-Zero X-DD coming to Wii U tomorrow!), throw some cool, new smaller titles at it (Mario Maker, Yoshi's Wooly World, Splatoon), and the occasional mega title (Zelda 201516) and it'll do just fine.