Totally agree with you: even if I never end up using the language, learning new idioms and patterns has been immensely useful.

I still make time to learn new technologies, I just find the physical act of coding to have rapid mental diminishing returns after around 40 hours. That probably isn't a big deal if you were running a startup. Code for a while and then attend to the many other aspects of the venture. Having a day job can really throw that balance off, especially when working for a company that doesn't waste much time with meetings and busywork (which is a nice thing).

Exactly. People call bullshit if I mention my sleep habits but there's something about learning new things that is so addictive. It's my joy in life certainly.