I'm late to weigh into this thread, but I may have a different perspective than most of what I've read above.
I've been playing my whole life (well, since I was 12). First inspired by the Ventures and the Beatles when they first appeared. Do the math on that. I did the cover band thing for many years starting in high school and later did small time regional tours with a few high spots opening for big acts. Then along came kids, grad school, more kids, career, and all of the usual stuff that sidetracks our musical dedication. Took long, long breaks during which I played very little.
BUT once they were all at least into the teen years, I redoubled my efforts with the guitar. I started getting up early every morning to get in 2-3 hours of practice before everyone else got up. Most importantly, I really tried to do a realistic assessment of what was holding me back technique and musicality wise. Kind of a do-over as far as guitar skills. The main things that I concluded were: 1) I was lacking any deep knowledge of theory so after all those years, I still didn't really know why some notes, chords, or harmony worked in context and 2) I had a lot of wasted hand motion, especially in my picking hand. I somehow got away with that in all the cover bands, but it was clearly holding me back if I intended to progress much further or to keep up my chops at all.
That 2nd item gets to the point of this thread. By concerted effort over some years (yeah, years), I reduced the excess motion in both hands to a small fraction of what it used to be. This has, and (i'm pretty sure) will continue to let me play fast, complicated passages that I absolutely would no longer be capable of if I was still trying to compensate with fast rather than efficient movements. The upshot is that I think I'm playing better now, well into my "eligible for Medicare" years, than I ever have. I'm able to pull off some Vai, Govan, and Johnson tunes and licks that I either couldn't play at all or played altogether half-arsed previously. PLUS, my fingers are no longer tight and sore after playing, and I need way less warm up time to start the tough passages.
Sorry to be long-winded, but I think about this stuff a lot. The moral of the story is this: I'm absolutely convinced that if you want to keep playing well, the single most important factor is to reduce finger motion to the absolute minimum necessary to positively engage the string. As Guthrie Govan said (in one his books, I think): when you watch really accomplished players, they're not moving faster, but rather they're moving less.
