I think what Made Kirstie Alley's Saavik better than Curtis' WAS that she wasn't as Vulcan acting. That seemed to be the whole point of the character in the 1st place, & why she's shown tearing up at the funeral. It isn't just that she's another Vulcan in Starfleet. It's that she's Spock's protege. Spock being half Human would logically have a protege within whom he can see something of himself, & that half of himself that he now recognizes is of value in dealing with such varied beings as he does
"Logic is only the beginning" is what he says to Valeris. This is why Curtis' interpretation of Saavik was not on the mark imho, & the character of Valeris WAS fit to that Saavik mold to a degree, though they retweaked it a bit.
So no, I don't think they should have tried to bring Curtis in to play it, but I might have been willing to entertain the recast of Saavik with Cattrail if they couldn't score Alley. However, Cattrail would have needed to drop some of the pomposity in her performance of Valeris in order to give the right performance as Saavik, and I could see why she might not want to have to