Same here, I mute the music and voices, and almost mute the other sounds (I don't mind a sound to register I clicked on something, or whatever), but that's about it.
I generally just turn off the BGM in RPGM games. Some VNs actually to benefit from the music in some scenes. I really only turn off SFX when a creator starts spamming them because "funny"
Also yeah the thought of adding ai voicing sounds absolutely fucking terrible, it already kills me that the girls have AI voices in the first place.
Depends on the game for me. It's almost always way too loud, but that aside, it comes down to whether it really does anything for the ambiance. It's a weak part of HH IMO--not bad, really, but it just doesn't do anything for the experience with very limited exceptions (and I think Runey knows this, as there are notes in the game to the effect of, "hey, you really might want to turn on your sound for this next part"). OTOH, it's very well-done in Eternum--I'd started playing that with the music off (after having played HH), and started over when I realized what I was missing.
Some VNs really have killer soundtracks, even when they consist only of the royalty-free music. Superhuman is a good example of this, thanks to it I discovered Teknoaxe, Myuu and few other awesome artists whose music happen to be royalty-free.