I feel like we're looking at this wrong. It's not a matter of whether Miyamoto is losing his touch or not, but how he functions. He's a creative type of person who is often questioning how people play things, trying to think of new ways to do things, making things fresh, and he's always been a guy about gameplay over story. That's why Miyamoto tries new things with many projects he works with. A lot of the games he works on having something new and fresh to them. He's a person who draws potential ideas and inspiration from concepts, game mechanics, and even from life for making games, which has resulted in some hit titles.
Though Miyamoto's need to create new methods of play doesn't always work, as some things he made weren't so great, such as Wii Music. Though, it's great that he continues to try new things, and this isn't just limited to games, but also gave suggestions for the DS and the idea of Miis.
Miyamoto also seems to have a knack to see the potential in other people's ideas, giving support and suggestions to help them grow, even now he had a hand in making Toad's Treasure Tracker a full fledged game. He's also helped with other games, little ones like... Pokemon, Kirby, and Metroid, and we know how some of those games turned out...
I could probably go on with this. He's great to challenge as well, which led to games like Majora's Mask and Link Between Worlds, with Eiji Aonuma wanting to make new games over remakes/enhanced versions. Sure, Miyamoto's getting old, is probably done with creating new hit IPs, and should retire, but hey, the guy still does some good work and is good to have around... Most of the time. Nobody's perfect 
Dance my pretties!
The Official Art Thread - The Official Manga Thread - The Official Starbound Thread
