I think there is only one thing that would have helped the show... have the writers take some lessons from the DS9 writing staff.
Doing this would almost instantly change the series to be greater than it was. I like VOYAGER and enjoyed it a lot, but it's possibly the one STAR TREK series that frustrates me the most because it didn't really get the mileage out if its premise like the other shows.
The one thing that DS9 did the best out of all the others was create characters that felt real. And they did this right from the pilot, and they kept that up the entire time. VOYAGER's pilot was really one of the best of the franchise... in some ways, the best. I truly believe that. But after that, it felt like they lost some fire, for lack of a better term.
I'll give you a more concrete example. Nog from DS9. He started out with very few scenes. But they were well done scenes, and this led to such a growth of the character that he really was a big part of the show by the end. And they did that with just some scenes peppered in here and there for years. It wasn't until much later that he got entire B stories or full on episodes about him. VOYAGER could have done that with their less used characters, like Chakotay, Tuvok, Neelix, and Kim. They did this a few times in their early seasons. But that was mostly abandoned by the time Seven came. You don't need to have a set amount of episodes for each person each year to make their characters real or more rounded. A little really goes a long way. Nog, Martok, Winn, Damar, Weyoun, Rom, Ziyal, Dukat, Garak... the list goes on. They all started with just a little, got some more, and became so fully formed and real characters that you forget entirely they are not part of the leads in the show.
VOYAGER could have done that with their actual leads of the series. This, more than anything, would have made a huge difference.