It is not broken, it does not need fixing, it is what it is and we love it.
ST:TMP is my favourite
movie of all time. It made me the ST fan I am today. But we can't speak for all.
But, for me... the Rhandarite ensign's line, expressing concern about Will Decker, is conspicuously missing from the theatrical cut. Originally, we only knew of the scene via the novelization and comic adaptation, or by ordering the script from Lincoln Enterprises. US fans finally got to see it in the US TV version, then the world, at looooong last, when the "Special Longer Version" reached home video. Eliminated again when TMP came to widescreen VHS for a boxed set, it was also finally included in the Director's cut DVD.
Billy Van Zandt put in so many months standing around the set in that alien makeup and yellow contacts. Imagine how he must have felt on premiere night, when that one meagre line had been dumped.
Spock's tears for Vejur (as the novelization calls the intruder) is also such an important milestone in the evolution of Spock. When I see the theatrical version now, I yearn for that scene.
I have no problem with multiple versions existing of TMP and it would be wonderful for someone to have another go at "completing" the movie that was raced to the Smithsonian Institute for the gala premiere. I really enjoyed the DE DVD release! Hearing the then-elderly Robert Wise discuss the film with pride, and discuss the changes, on the commentary was amazing.
By the way, if you turn English closed-captions on, on the DVD DE, the transcriber mishears Robert Wise - and has him stating that the premiere was at the "Swiss Odeon". Hilarious.