From what i herd it wasn't Alley herself that asked for a massive increase in salary for ST III it was her agent.
It's
always the agent. But... Paramount deliberately offered less money for ST III than ST II, giving the excuse that "sequels usually made less money". The agent rightly made a large, silly counter offer, fully expecting Paramount to drop it to something similar or larger to her ST II salary, as would be common practice. But... contractually, Paramount only had to make "an offer" and they were now totally clear of Alley's original contract. Meanwhile, Alley was offered a starring role in a stage play ("The Glass Menagerie", IIRC) and, at this time in her career, the female lead in a play was better for her CV than a sequel to her first professional (supporting) movie role in showbiz.
Nimoy was really happy with Alley and she loved being in STII.
But...
Shatner was not. In my interview with Paul Winfield, conducted
before ST II had been released - and long before anyone knew about the ABC TV version (with that alternate Kirk/Saavik flirtation scene) - I can tell you that he said, of Shatner and Alley: (paraphrasing) "I can tell you that their off-screen relationship was quite the opposite of what you see on screen."
The sadness was that they did not add the sequel addendum to her original contract. That is 101 for new stars.
The contract had the standard clause. The studio had to make an offer on a sequel. They could force her back to a sequel by simply paying a sensible market price for eighth banana in an ensemble cast. Paramount played her agent for a sucker, I strongly suspect, because Director Nimoy had already decided to recast. And to reconceive the character while he was at it.
I don't like Kim Cattrall as an actress, I don't like her voice, and her dumb hairstyle and hairband made her look like a Vulcan with a fat face... For me, Saavik is Kirstie Alley or nobody.
Hehehehe. Had Alley done ST VI or "Cause and Effect", you might have still gotten a Vulcan with a fat face.
Alley says that, when she played Saavik in ST II, she was the thinnest she'd ever been in her adult life and that was because of the fatal car accident that claimed one of her parents' lives between final auditions.