They need to just stay the course and continue to release great games at the quickest rate they possibly can. As the Wii U becomes cheaper to make, they can continue to reduce the price. People will buy it as a secondary system for first party games.
Launching a year early was an advantage for the Wii U because Nintendo can launch a new system significantly more powerful than the PS4 in winter 2016/spring 2017 and they wont be criticized too harshly for it. Perhaps by then, VR will be much further along. Hopefully they are smart enough to drop Wii from the name next time around.
The 3DS is doing fine and many first party games have sold over a million copies. It's going to be huge money maker for them over the next 2 to 3 years.
People who think Nintendo should go third party are very shortsighted. There is some small momentum growing and next year the Wii U will have Donkey Kong, Bayonetta 2, Mario Kart 8, Smash 4, X, and I'm sure other unannounced (Animal Crossing?) or little shown titles (Yarn Yoshi / SMT x FE?) released. Things should improve a bit.
I would suggest to Nintendo that there a few small things to help sales to their current audience. They need to seriously beef up the Virtual Console. We want N64, GBA, and Gamecube games at a minimum. I understand they don't want to release every great game in one shot, but I doubt games like Baseball and Urban Champion are selling huge numbers. Second, release sequels to games we haven't seen in a while. We want new F-Zero, new Wave Race, new Star Fox, new Earthbound, new StarTropics, new Advance Wars, new Pilotwings. The casual audience who bought Sports, Fit, and Party are gone so stop focusing on them. Third, why not put a legitimate Pokemon on consoles, even if just a remake? We know it's not going to put up portable numbers, but it will sell systems and the gamepad would work perfectly for it. How about helping Level 5 port the Layton games and Ni No Kuni? Last, they should publish as many exclusives as they can stateside. Puyo Puyo Tetris, Taiko Drum Master, Dragon Quest X, etc. The games themselves may not make a profit for Nintendo, but they'll sell some systems and those buyers will buy other Nintendo games.