I don't think they should change who they are. From what I understand they are doing just fine and the niche they have carved for themselves is serving them well. They should stay where they are, in my opinion, because we already have enough channels for adult oriented games. Even the head of Sony once said that they are not in direct competition with Nintendo and that he found them to be necessary for gaming to survive because they were the ones introducing kids to the industry.
The Wii U wasn't Nintendo's best move, as they're quietly hurting, but I don't think having the company produce more adult-themed games is going to help them. From the sound of it, Nintendo is making their money because of these 'kiddy' games, such as Mario and the Legend of Zelda, if that is what you're referring to. Games like those might be turning you away, but these games, in my opinion, seem to be keeping Nintendo and the Wii U afloat. Mario Kart 8 is also doing a good job of helping Nintendo.