As the series went forward the actors seemed to stop playing their characters and start playing themselves. This was never more evident than with Shatner himself, who undergoes a definite shift from "Kirk" to "Shatner" somewhere around The Voyage Home. Possibly even as early as TSFS.
I'd have accepted the mind rape better if Valeris had been Saavik. Spock's un-Vulcan-like feeling of betrayal at his protege just doesn't have the same impact given we've only just met her.