I was working on a canon character profile and was struck with this thought. What if the fuku designs kind of signify the unity of the senshi? (Please bear with me. I am trying to control my thoughts and this came out!)
At the beginning of the series we have Sailor Moon who is joined by Mercury, Mars, Jupiter and then Venus. All of them have generally the same kind of style of fuku. The only variation is pretty much their shoes and colors.
When they meet the outer senshi, there are a lot of differences in their fukus compared to the inner senshi: darker colors, variations of the length of gloves. Pluto has always been a little more sympathetic towards the inners (although still as resolute about the killing-Hotaru thing), and her fuku is more similar to the inners than Neptune and Uranus who are very vocal about their dislike towards working with the inners.
Then Saturn, the most estranged senshi of them all has even more differences: winged shoulders, heart crystal brooch. She is feared and was almost killed before she could even be awakened simply because of her powers.
But as the series progresses everyone's fukus kind of get more and more similar to one another until, at the end of the manga, their eternal fukus are nearly identical besides that of the coloring. And at this end, I think it can be said that all of them are much more at ease and they all want to work together. They're a unified *team*. And I think the fuku reflects that.
Now, people might have come to this conclusion before, but it struck me just now, and I was curious about everyone else's thoughts!
(Sorry if this is rambly, but I hope I got the point across!)