I love a good animation discussion!
I think that is fairly subjective; take the Chuck Jones period--celebrated by some, but it could just as easily be read as "lazy" work once the mono-colored, abstract backgrounds (or UPA influenced--since he produced work for that group) backgrounds became the norm at Warners, instead of the rich, detailed backrounds regularly used in the early Merrie Melodies/Looney Tunes short subjects.
You're thinking of the work of Maurice Noble in the 50s, which is most certainly not influenced by UPA, nor lazy in any sense of the word. It's overwhelmingly celebrated in the animation world (and some would say far too often imitated).
On the subject of replacing the original animation in the Star Trek Animated Series... I can't say I feel strongly one way or the other. Part of the charm of the series is it's junky limited look, which feels right at home with the storytelling style utilized. On the other hand, being open to new interpretations can sometimes bring surprisingly great results.