Let's build apps like Yo. They're good practice. Doing silly things that amuse oneself is a critical component of hackerdom. Let's just not fund them.
We all know that those silly apps/games/etc aren't solving any big world problem, but neither are watching TV, browsing cat gifs, etc. What we do during our chill out time is up to us, and I'd say there are way worse things to do than coming up with silly coding projects.
Let the Yos and fart buttons of today help these developers improve their skills in a fun way during their spare time, so that tomorrow some of them might be able to move to those big problem solving projects.