It's quite funny that TUC cost $27 million, LESS than TFF, but TUC still looks so much better!
I think $27 million is a little low; the production budget in the Nick Meyer papers lists the cost of the film at $29.16 million.
I think it looks better for two main reasons: (1) ILM did the visual effects and (2) the darker color palette was more forgiving than Shatner's brighter tones. Shatner's picture actually had a lot more location photography than Meyer's.
Meyer's film also exerted a little more effort than Shatner's in redressing the Enterprise-D interiors, which helps.
Still, it has a lot of flimsy office chairs at the end.