I'm still using it.
They recently just released an updated, adding some more social interaction (Ask Central and Style Central) and a bit more customization (you can decorate the walls and floor now.) You can also send messages to your friends and create up to 100 'Sidekick' Miis to share with others.
Really, it's just more of the same with a couple tweaks. So if you've already lost interest I doubt they've added anything that will bring it back. I'm really only using it for the Miitomo coins. It's not like it's a huge time investment to get them or anything.
