A bit of an update, after the whole brake MC misdiagnosis at Subaru City.
Despite Subaru City NOT having bled my system as per my request during my second visit there (after having cited safety reasons for it), I have driven the car as it was until a few days ago. The new pedal assembly that was installed during my second visit there stiffened up things a bit, but in warmer temps, the pedal feel was still sort of mushy and soft. When I mention warmer temps, I'm referring to how the pedal felt after having the car parked in my room-temp underground garage overnight.
Fast-forward to a few days ago and it just so happened that I would be in Calgary for a few days. I figured this would be a good opportunity to have Vex bleed the system with Endless fluid as well as install some Endless SSY pads along with some Goodridge Phantom lines, which I provided (going on SubiSpeed's recommendation that they'd fit the 2015+ WRXs). I was told that the rear Goodridge lines did not fit exactly like the stock ones did, meaning that there's less of a bend which might put some tension on the lines. The hoses and their corresponding fittings are made of pretty durable materials, so I'm pretty confident that the rear lines won't give me any grief.
After the lines and new pads were installed along with the system being bled, I can say right off the bat that brake pedal feel is 100% better. I broke in the pads as per the outlined procedure to the best of my ability, and they can't even be compared to the stock ones. I barely depress the brake pedal and I feel them grabbing.
However, on the clutch note, the pedal feel is still sort of mushy and soft, even more so after the car is parked overnight. Along with that, I noticed that while driving in colder weather and shifting, the clutch pedal has a harder time coming back up to its resting position. Ryan @ Vex has kindly agreed to re-bleed the clutch slave one more time (free of charge), to be certain that there is no air trapped in there.
I'm not sure if this has to do with the fact that the reservoir is shared between the brake and clutch MC on the new gen WRXs, making the bleeding process a bit more of a pain and more susceptible to getting air in the system. On the other hand, if the clutch pedal is still on the soft side after the second bleed at Vex, I'm going to go on a limb and say that the clutch slave will probably need replacement.
That's about it for the "short" update. I have updated the first post as well, to reflect everything that has been done to the car since my last update a while back.