To read or not to read that is the question?
In the thousands of students I've taught over the years I can report that sight-reading has never been a top priority for the majority of guitarists. I have seen many start with a keen interest only to lose it in just a very short time. I believe a few reasons that are key to guitarists failure but maybe overcome if the desire to sight- read for the right reason.
I've found a lot of students come to me from other instructors with stories of only being given a page out of a particular method book to workon in class and they work all week on ex."aura lee" resenting it or not picking the instrument up at all until they find a teacher who will listen to what they truly want to learn. So in I would give them a cool pentatonic, teach them a 12 bar blues, and slip in theory unbeknownst to them.
Soon that same student would be playing all styles. know cool 7th chords up and down the neck and have a repertoire of several songs from memory. The sight-reading would be well on the way too.
The guitar presents we players with many joys, numerous false starts and hurdles, the largest is themain hurdle for some readers and players. That would be position shifting with en-harmonic notes. Simply put, we have the same pitch on various strings in a number of places which complicates matters for the player.
Traditionally method books would star reading in 1st. pos. in C position CAGED no reference to that system by default, but MI are teaching in 5th pos. as that always has the geatest range up to C on 8th fret. Check out that book and then practice reading tunes out of "the Real Book" instrumental blues and jazz repertoire bound to help sight-reading.
Sight-reading for guitar-MI Press
The Real Book- Hal Leonard
These are invaluable resources guitarists, musicians out there.