That's why you play around with new technologies in your free time. Then, when it's time to build your next big project, it's not "I have three years experience with X and none with Y; which should I use?" but rather "I have three years experience with X, but I've been playing with Y for the past year and I think it's a better fit."
Yes, yes. The problem comes when you don't have much free time. When you're working on a successful project, it will consume every hour that you can devote to it. If you then want to have a life outside of computers, you find yourself having to make a conscious choice between your main project, and learning new technologies.
This problem becomes far more acute as you get older. When I was in college, I had all the time in the world to experiment with things. These days, I don't have much energy for computers when I'm away from work.
