I like that question! I had a whole class on psychometry this semester
I spent 500$ on these modifications and 2000$ on a new diy DAC. The new DAC made a huge difference of course...
The Vcaps brought a big improvement in detail and timbre, which became fully evident only when I replaced the 0.1 caps with mundorf's supreme. The 2k7 from shinko revealed some more.
Attenuators made everything more coherent. Same with bypassing the source selector. SIlver input wire 'takes away a veil' compared to the original wire.
Of course everything is not just more detailed now but also much more enjoyable, although it was pretty enjoyable to start with. I particularly salute the tightening and detailing of the bass, which seemed a little unassuming and bloated in the beginning. I also salute the timbre which is to die for now. And also the detail, which makes the music come through, and alive.
The layering is far more diverse and identifiable. Soundstage depth hasn't budged an inch though...
Also, after the Vcaps I noticed surprising dynamic changes in places I know by heart. A tom tom strike in one channel, a guitar note, they come right out at you in the foreground. There was none of that before.
Dynamics, but also detail, seem to be crucial to enjoyment.
All in all I feel I own a little gem.
Subjective improvement, as far as I am concerned: from 100% to 150-180%. I don't know what more I could want, but I also don't know what is out here.