I never really got her motive for being apart of the conspiracy. Peace, to me anyway, seems more logical than war, for the most part. Especially in the kind of situation the Federation found themselves in with the Klingons. Sure I can understand if there were Klingons who would want to fight but a Vulcan? I don't buy it. So I imagine Valeris as actually being a Romulain spy, since their motives are pretty clear.
As for Saavik, sure she would have been more of a surprise but it would have seemed like a cheap stunt to me with no real basis for her actions. I mean if Kirk can get over his prejudice, based on the events of STIII, then surely Saavik could as well.