Alley in III would’ve made it feel like a true continuation of II. She mustve done Runaway instead of ST III. picture Alley in Trek III and the movie gets better - all the stuff on Grissom, then with young Spock, the chemistry with David, his death scene wouldve been even more powerful, telling Kirk his son is dead. the scene of Savvik and Kirk on genesis, and that glance between Spock and Savvik at the end. (like the Savvik in III shed have probably had her hair all long/permed like in Runaway

)
http://cineplex.media.baselineresearch.com/images/261767/261767_large.jpg
if Alley had done III she wouldve had a cameo in IV (or maybe shed have been part of the crew?) and the Valrius role in VI (as it was originally intended to be savvik - Meyer wanted Alley back but she declined, and Robin Curtis wasnt considered. So it went to Kim Cattrell who had been the original choice for savvik in Trek II) it wouldve made alot of sense since Savvik wouldve watched Klingons kill the man she had some kind of emotional bond with (imagine sitting there in the cinema xmas 91 watching Kirk and Spock interacting with Savvik knowing Meyer is calling the shots like its 82 all over again! itd have been like Wrath of Khan part 2! plus the shock of her being behind it would’ve been such a huge deal)
but since things happened the way they did and Alley didnt return, maybe they shouldve just cast R Curtis as Savvik in VI instead of creating a new character (wouldve been cool had Alley done it - tying in with TWOK and all, but seems abit harsh not wanting Curtis there since she had taken over and since VI was bookending the Genesis 'trilogy' and it was her version of Savvik that witnessed Davids death at the hands of the klingons which would’ve been the ideal reason for savvik turning traitor - anyway audiences would’ve been abit like 'eh WTF? Alleys back as Savvik?')