The TMP uniforms do look dated. As someone else mentioned, they are the 1970s view of futuristic...which is now a retro view of futuristic. I'm sure at the time they were awesome.
The dark red uniforms that followed, on the other hand, hold up very well. Instead of trying to be futuristic, they're trying to be militaristic. I know Gene Roddenberry didn't like that direction, but to me it really worked well as a "look," regardless of the inspiration or the implied meaning Nicholas Meyer was going for. It's more unified and just worked better on film in my opinion.
The ST2+ uniforms seem dated, too, just in a different way. The '70s look of exaggerated styles, synthetic material and informality had given way to the return of more traditional styles, natural fibers and a more status-conscious formality. Reagan brought the morning coat back to the inauguration, people were getting fashion ideas from The Preppy Handbook
Military styles tend to be conservative and resistant to change, and going to a look with more retro military cues may be why the TWOK maroons seem to age better for some people. But they don't for me, they just seem like a cluttered, over-styled attempt to cram a bunch of quasi-military cues onto one costume. Conceptually, TMP is the high water mark of Trek uniforms.