I don't know about anyone else, but one of the things I liked particularly about TNG and DS9 is that we got to know various alien races much better than we did any alien race in TOS. This started with the Klingons in TNG, of course, and culminated with the Bajorans and Cardassians in DS9. ST is science fiction, and a certain amount of technobabble can be way cool, but it's all for nothing if the characters don't work. Of course, ST is differentiated from other great science fiction sub-genres wherein there are no alien races (a lot of Asmiov's works, for instance) - so characters can differ from one another in really fundamental ways, and this is something that could have been exploited in a show like STV.
Voyager was trying to get home by traversing an incredible volume of space, a volume much, much larger than that occupied by the Federation, which itself was comprised of dozens of different races. If I'd been in charge, this is how I would have taken advantage of this:
Part of the show's bible would have included a statement to the effect of,
"Over the seven year arc of the show, the Voyager will pass through a volume of space that would contain dozens, if not hundreds of volumes comparable to the volume of the United Federation of Planets; some of these volumes will be occupied by similar federations, unions, conglomerates, empires, etc, of many species, while others will be occupied by a single species who expanded to occupy what was, for some reason, space empty of other intelligent species or who annihilated the other species they encountered. As Voyager passes through these volumes, we will get to know these species the way TNG and DS9 allowed us to get to know the Klingons, the Romulans, the Bajorans, the Cardassians, and races of the Dominion."
Every summer I would have wrangled the writers into a secluded location and said, "OK, people, this year we're gonna pass a couple of volumes equal to that of the Federation. Who occupies these volumes?".
So, every half season, I would have had a federation, union or empire, or some unitary species that would have been the centerpiece of, I don't know, three or four shows, so that we could really get a feeling for that species or federation (or union or whatever) species.
Sure, a few species might span the entire series, _e.g._ the Borg, the Vidiians, Species 8472, and the Hirogen Hunters. But for if I'd been in charge, I'd seen to it that we really got know, the way we did the Klingons and Romulans in TNG, and the Bajorans, Cardassians and the species of the Dominion in DS9, a couple species EVERY season of STV.
Anyway, that's how I would have improved Voyager.