First, the 3DS has to compete with the DS, and I have to wonder whether the market really sees the difference between the two yet. The Wii had a fitness hook during our cultures highest health craze, but for many lays unused as though it were a thighmaster, or other ‘as seen on TV’ peripheral. The core market probably owns a 360 or PS3 in conjunction to the Wii, and their expectations are mounting due to innovations in online functionality and interface design. The Wii-U has a large number of issues to address.
Here’s some ideas:

Look at smaller developers and get a more solid arcade/PSN game solution. Fund a few smaller exclusive projects from creative third party developers.

Stop trying to turn interacting with your friends into a gimmick. Get a simple system that works while giving you basic communication and game connection. Gimmicks must be discreet and optional.

Use Mario as a spokesman to promote third party games. He is probably Nintendo’s biggest icon and one could use him to draw attention to new and interesting things on the platform.

Be a little more visible, competitive. How many times is Call of Duty advertised on TV? A smart Nintendo commercial could do alot for their brands. Maybe have Nintendo characters parody other games? I don’t know. Hire a better marketing department. Kevin Butler was a big hit for sony, and I think humor is a good way of hooking people.

If Nintendo doesn’t push themselves into the enthusiast’s mind share who will promote the Wii U? Your mom?