I think Robin Curtis' role in "Gambit" gives us a bit of a taste of how a traitorous Saavik would've looked.
Novelization aside, Valeris' specific reasons for opposing peace were never made clear, whereas after the events of STIII, it would've been easy to understand Saavik's reasons. Valeris' line to Kirk of "they killed your son" would've packed more punch coming from someone who knew him and witnessed David's death.
I think the consensus among fans is that this was a missed dramatic opportunity. I don't know who was responsible, and, honestly, I doubt we will ever conclusively know.