With one caveat:
>Always hone your skills so that when an opportunity arises, you can pounce.
My strategy has been to follow my passions, which include digging into various technologies that interest me. I don't do it "so that" I can be relevant. I do it because it's fun.
It just happens that, when you get good enough at enough things, you'll find that at least some of those skills are in demand. I know a lot about so many programming topics that one coworker just accused me of having "an encyclopedic understanding of just about every topic."
A lot of people have their curiosity tortured out of them by their experiences in school. Anyone reading HN likely is at least on the road to lifelong learning, so anyone reading this is likely on a path that could result in a strong salary. To those who complain that reading about every latest new technology is boring, I say: Find your childlike curiosity and reclaim it.