My sig says it all on my belief in the part of music in our lives. That being said, I never felt like we simply have the ability to express it freely. That is, until we learn how to express it freely. I can't speak from your shoes but can offer insight into mine. When I felt like my playing had gotten to its limits, I endeavored to learn the fretboard (It sounds obvious I know) because a ton of guitar players honestly don't know it up and down. It's easier than you think and once you know it, the scales make sense. You understand the language they speak in a sense. Once you understand that, you have the free ability to express yourself on them strings.
I love the previous posts also, it's important to be yourself on the guitar. I've always been thoroughly impressed with how many players put their own style on music. It's just amazing. Remember little brother, if you don't express yourself on that riff machine, no one else will. You have an obligation!
It's funny, because the fretboard is a finite number of discrete notes (discounting the fact that the strings can and do make it everything in between), but something in our heads (well, my head - I can't speak for everyone) makes it seem like so much more than it is. After a few years of playing, I haven't mastered the fretboard, and I think it's only because of this daunting and complex image I've painted of it in my head, not because of real complexity.
On the other hand, I spent a few years "learning" piano where the scales are laid out literally in black in white in front of you, and I kind of suck at that - I didn't practice enough to not suck, TBH. But for some reason unknown to me, I find the guitar more intuitive. However, I'm still way better at buying guitars than playing them.
On the guitar, each fret is a single note. They're even in order for us on any given string no matter what it's tuned to, so it should be easy to master the fretboard, right?
I struggle with this internally. The reason I think I failed at piano isn't just the lack of practice, but maybe because playing it is like playing both rhythm and lead at the same time - one with each hand, whereas guitar is either or - with notable exceptions like Eric Johnson, Jimi Hendrix, Stevie Ray Vaughn, Wes Montgomery, Steve Vai, etc. My point is you don't have to be able to play both parts.
Let's see, where am I going with this? I don't remember.
i think I was just saying that mastering the fretboard shouldn't be difficult and that we (or maybe just I) make it more difficult by holding onto the impressions we had when we first looked at a guitar - all those strings, all those pieces of fret wire, how hard those guys must be pushing down to create a note (that might actually be from playing on my $50 first guitar where no amount of pressing rang out a clean note).
So while it's a game of muscle memory, I think it's at least equal part a mental game that I've yet to truly overcome.
Looking at the thread topic, maybe that's where I was going with this, maybe not. I'm not sure.