It would have been a good kind of bad for me. I liked STII Saavik, it sucked that her story essentially dies in STIII. I never liked Curtis as Saavik, not that she is a bad actress or anything but her version was too Vulcan ignoring the Romulan aspect Alley brought to the role. By STIII she was like a extra in the movie, completely flavorless, as a traitor in STVI she might have gotten her passion back. I agree with previous posts, Saavik has a reason to hate Klingons. In deleted scenes there was hints that Saavik had a little crush on David or a hint of a relationship. Seeing him killed for her would leave an impression.
I would hate to see her as the "bad guy" but it would have made a lot more sense. It would have paralleled the same conflict Kirk was having regarding David's death. It would also have given us some closure on her character which pretty much disappears after STIV for some reason? I mean they did not consider making her a crew member on the Ent A? Especially considering Sulu was promoted to captain of the Excelsior.