Okay, let's try again.
Putting all the "listening"stuff aside (as valued as it may be) the intent of my OP was to see what 3 specific things might improve my playing.
Well, listenting WILL improve your playing...
Okay, let's try again.
1. Scales (which ones are most useful for the rock / blues bassist?)
The diatonic major scale. But understand that to "know" any scale means:
A. You know the whole-step and half-step arrangement of the scale.
B. You can figure out the notes of the scale in every key without an instrument (using the correct enharmonics), and even better without paper. NOT memorize the notes in all 12 keys, but KNOW them because you understand the way music works.
C. You know how to find those notes on your instrument (again in every key, and not by relying on a picture or TAB) over two octaves.
D. You can sing the notes of the scale so that you know what the next note sounds like before you play it.
2. Theory (what specifically?)
A. Basic harmony of the diatonic major scale... after you KNOW the scale (see above), then you need to sit down and learn how to build the four-note chords from each note of the scale.
B. Be able to figure out the notes of basic four-note chords, without using an instrument. You should be able to see a chord progression and think through it to know what notes are in each chord, and how they go together. That means you should know how to build a major triad, minor triad, diminished chord, augmented, dominant 7, minor 7, major 7, minor 7 b5, and understand the extensions above the 7th.
C. Be able to find those notes on the neck and play the arpeggios of a chord progression.
D. Understand the use of Roman numerals to designate chord relationships. Know WHY "ii V I" defines the key center, how the ii is related to the IV, etc.
and for #3, I say learn to SING everything you play. Fix it in your head. Don't do endless repetitions of running scales up and down, that's only physical learning. You need to have your ears leading your fingers. So if you sing everything you play, then your muscle memory is going hand-in-hand with your aural learning. Bottom line is that to be the best player you can be, the MUSIC must come before the instrument. So MAKE the music guide you instead of learning the pentatonic minor and riffing on it all day.
Here's a great exercise... Sit down with your bass safely locked away in its case. Sing a nice melodic solo over a 12 bar blues. Record it. THEN pick up your bass and learn to play it EXACTLY like you sang it. Not just the notes, but the phrasing, the inflections, the dynamics, the slurs. If you can get that skill down, and you listen to a lot of great players, you'll be well on your way to becoming a great player yourself.
John