Don't the two go hand in hand with improvising? I think they can, and do, but they don't have to. I prefer expression over musicality, personally. It also depends on your goal at the time. Sometimes it could depend on your mood, or your current project. Other times it could encompass your overall view on the instrument. I tend to take the last approach. I have varied at times but always preferred expression over musicality. This is why what I've been producing as of late falls in with this pursuit.
I can't put myself in someone else's place but I would imagine that letting go of musicality to devote yourself to expression is not an easy task. It surely is not a popular one, that is obvious just by observing any person at random and their musical tastes, let alone consulting the charts.
What is involved in this is not a certain set of scales, or a specific key signature to drone off in. It doesn't involve any special technique either. All it requires is (and this might be easier said than done) for you to throw away every rule and every rigid thing you abide by when composing or even improvising in a traditional sense. This is not about playing along with a jam track, or even anyone else (although it is entirely possible and even quite fulfilling when among welcoming and like-minded musicians). This is just about you, and your guitar. How much at ease are you when you've thrown away all references and familiar starting points?
When you decide to walk down this path, what comes is a more primal connection to the pick, strings, the frets, and the notes. You begin to notice your physical limitations as well, but those limits will be conquered soon enough because your connection to pure expression demands it.
Let me just say that your results and depth of experience here will all depend on and differ with your background and foundation with the guitar. Meaning, your actual skill level up to this point and how you got here tracing back to your very first days playing. To put it in another way still, what kind of training have you had? The better your foundation, the easier you'll be able to set off on this course. If you have a weak foundation, specifically in finger dexterity and comfort on the fretboard as well as a hindrance in tremolo picking (or any limitations in your picking really) then there will be obstacles. Nothing insurmountable, because time will overcome all in this, yet there will be obstacles nonetheless. Let's say you decide to persevere, you will learn a great deal about yourself that you can then apply to whatever you wish, or you can simply continue on and go as deep and as distant as your devotion will allow. There are no limits here. Conversely, if you do have a strong enough technical foundation you will overcome your own obstacles a lot quicker, and feel much more accomplished with each one because you will also be surprised at the types of obstacles coming your way.
What kind of obstacles? They are not the same as when learning a new song or piece. They are not the same as when you master a new scale or even apply that scale within a particular solo approach for a certain song or piece. It won't be the same as when you might discover a new sound on an effect pedal and a new application for said sound. The obstacles I am referring to are connected both physically and spiritually. But don't be swayed or pushed away by the term "spiritual". I would have to assume that if you've been following me this far, you aren't afraid of such a term or its association to guitar playing. Expression is undoubtedly something spiritual, whether you want to use another term or not that's fine, but we are reaching deeper than normal here. We are trying to connect to a place that is inside us, that is infinite when it comes to creation in music. It may not be as refined as woodshedding a riff, or song structure, but it is quite magical.
Let me draw some parallels from other players I've heard speak on this subject over the years. Only two quick examples. First, Carlos Santana. He once said that there was a time at night, mainly after 10pm where he'd just plug in and "cast off" as he put it. Second, the teacher of Ravi Shankar. I'm sorry I don't remember his name now and forgive me for not researching it, but his name is beside the point. This "guru" of music if I can borrow that loaded term said that playing an instrument, even music itself was only meant for prayer. As you may know, classical Indian music is heavily based on improvisation. Using your instrument to express yourself and improvise, to connect to that infinite well of creativity, can be called a prayer if you look at it his way.
Every time I pick up my guitar and play, I have one goal in mind. To explore, and burn the bridge I've just crossed because I know there will be another bridge ahead.