Yeah, what Christopher said! :)
I actually don't spend time on a skill or technique unless I already have an application for it in mind. I have limited time I can spend on learning so I try to use it wisely. I am also of a personality type that doesn't like learning things I won't use. I was the kid whining in shcool about "when am I gonna use this stuff" :).
As an example, I've wanted to spice up some of my soloing with both speed and scales other than the pentatonics. I chose some solos as examples experimented with ways to expand upon the pentatonics, mostly Dorian mode. This approach keeps me motivated rather than sitting down and doing speed drills or learning all of the modes.
My speed lead example is YYZ by Rush. I swear the day will come that I will be able to play it for real (master it). Even though I'm not there, it has helped my speed, accuracy, picking, and muting technique. So even though I haven't mastered it, it's useful as Christopher points out.
I have also found that just learning a pile of songs helps my playing in general. For example, I learned Mystery Achievement by The Pretenders recently. At the end of one of the solos, there's this galloping thing he does through the scale. It was a struggle at first but now I can do it without thinking about it. The bonus (and it's a big one) is that it has become part of my playing and I've had some "whoa, where did that come from" moments. I can now alternate pick through part of a scale across strings fast...I've been struggling with that for YEARS. So learning that song helped me break through a significant barrier.
The point is much of what you need to know is there in the songs. Whether you go to the song before or after learning the technique...the song is still involved, and that's what it's all about...making music.