With respect to the original topic:
Watched it again for the first time in decades if honest, I have to say it's still great fun but I wonder if the budget was reduced.
Yes, the budget was reduced. This is painfully evident in the egregious reuse of TNG's engineering set.
It seems they blew half the budget on the opening explosion. I still think the opening sequence is one of the most exciting bits of the film. They could have crafted a whole movie around George Takei and "The U.S.S. Excelsiorrrrrr."
On the other hand, they had enough of a budget to pull off some decent hair, makeup, and wardrobe for the Klingons. TUC is really the first time they are convincingly realised on-screen as a motley band of diplomats, statesmen, generals, soldiers, lieutenants, lawyers, and saboteurs. TUC is Klingon-crazy, and rightly so!
But there is a TV-movie-style cheapness that pervades the film. I mean, it's a Star Trek movie sequel, and a Nick Meyer movie at that. Rura Penthe mostly looks like a TNG planet reject (though there are some nice wide shots when Kirk and McCoy are escaping), while the peace conference at Khitomer is apparently taking place in
Zordon's Command Center. The latter of which would find its way back into Star Trek a little later in the TNG two-parter "Descent". Speaking of which...
TNG manages to spread its seed all over the movie, from Michael Dorn appearing as Worf's grandfather, to the heavy re-use of TNG sets for the interior of the Enterprise-A (which bears so little in common with the Refit Enterprise internally that it's hard to believe it's the same endoskeleton), to a cameo appearance by Ten Forward as the President's office on Earth, to the appearances of Mark Lenard, Leonard Nimoy, and James Doohan who showed up as those same characters in TNG episodes around the time of the movie's release (in "Sarek", the two-parter "Unification", and "Relics" respectively). Indeed, "Unification" has the same basic premise: a peace-making Spock, trying to bring a classic TOS enemy into the Federation. I guess you could be charitable and say all these links were appropriate. The baton was truly being passed.