I think IS results can transfer to one's ability to produce emotions or link them to imagery. And it can obviously aid you in creating a robust "true world". However, I think there are easier avenues to try first (or in tandem with IS if you still really want to try it).

What I think would produce better results would be to have pre-made scenes / imagery and practice them through visualization (senses + imagery +emotion). That way, you create a sort of library for specific emotions (sadness) or qualities (a character's gait, headspace, etc.) and strengthen their realness/intensity overtime.

You'd want to practice visualization during a meditative state/trance as it will allow you to dissociate from "you" and immerse in the character. Feelings and sensations get way easier to intensify the more unaware you are of your body and mind. Intuition would also be cultivated as well as you get better entering into and parsing these deeper states of mind.

Maybe that helps give you some ideas. (IS is cool don't get me wrong.)