Playing a Vulcan is extremely difficult as we've seen for nearly 50 years. To deliver dialog in a near deadpan and still be interesting must be extremely frustrating for an actor. To date, only two have pulled it off perfectly: Nimoy, who defined the Vulcan demeanor, and Mark Lenard. Others who were cast as Vulcans were at best trying to copy the two best examples.
Kirstie Alley, Robin Curtis, and Kim Cattrall did a very good job in their own way, but I liked Cattrall's take better than the other two. She was a Vulcan, but not just a reasonable facsimile of Spock. She was her own character. I think Nick Meyer was right on target wanting her for Saavik in the first place.
Too bad that he couldn't make it happen for TWOK, but then again maybe the timing was just right.