I'm fascinated by software that's stood the test of time. It's a source of inspiration, an aesthetic. It's a noble vibe and way of life. Developers who write venerable software have spent time on an incredibly high leverage persuit.
Battle tested software projects that don't bend to the latest fad are always worth studying. New ideas are often reified old ones, and keen developers who get that have a leg up.
An example of what I'm talking about might be Emacs, MySQL, Java, or C. I realize each of those was once a shiny new project; however, today they are all what I would consider venerable. Great technologies not made great by marketing, but by their own merits.
I see many developers getting excited about new tools, methods, designs, or technologies. There's nothing wrong with being excited, I get excited too. But when it comes to making pragmatic choices, a technology's track record should matter a lot.
But then how do we foster innovation? How do new ideas get traction? Just because it worked before doesn't mean it will work best moving forward.
Not all decisions need be pragmatic! When failure is an option, or fun is the objective, take risks! In other words, use your side projects to try out that shiny new library.