I think that's true, Les, that layering too much "texture" can indeed detract from a pure and spare vocal. The vocalist can add texture of his/her own, can energize the song with more ornamentation, emotion, unique phrasing, etc. which can "punch up" the energy of slower tunes as much as (or more than) a more complex instrumentation...

(this from a singer who has done a lot of "arranging" in groups I have been in, but does it with intuition more than "musicality" if that makes any sense; i.e., knowing/feeling what sounds "right")

good luck with your project; sounds fun! Makes me wish I was in a band again...

Peg