Yes they can. They need to make "Wii games." Game like Wii Sports and Mario Kart.
Motion Plus is how you do it. People bought the Wii for motion control games. They wanted to be swinging and clashing swords. Game like Skyward Sword can increase sales, if it focuses on quick, fast gameplay and no puzzles. Other motion gfames can help too, like a Starfox Wii. It comes down to making Wii software, which is something Nintendo hasn't been doing.