since sea of stars has very prominent chrono trigger influences that it wears on its sleeve so hard they're practically the whole shirt, i want to talk a little bit about the mechanic of new game+, which really reached prominence with and was named by chrono trigger
one of the things that made new game+ powerful and interesting in chrono trigger was that chrono trigger gave you access to the final boss really early in the game. this was a wonderful choice on the first playthrough! how many of us looked at the bucket, made a save, and then went "i'm gonna take a swing and see what's up"
and you get absolutely waxed, there's no way around it at that point in a first playthrough. and for the rest of the game, lavos is just hanging over you, taunting you. if you're like me, you throw out some checks as you progress. am i getting closer? how far can i get this time?
the entire game you know that if you were strong enough you could just go save the world. and since you're not, lavos is this menacing presence, because you know your enemy firsthand.
and when you get the chance, when you're unleashed upon new game+, you get to not only do it, but immediately find out that something is different—beating lavos early isn't just a power trip. there's a new ending waiting for you. wonder how many of those you can find by killing lavos at different points in the game!
new game+ is compelling because there's more to do, more to find, stuff worth carrying over
very few games do new game+ well because they miss that core, essential aspect of the design. you're just starting over with bigger numbers and more stuff
and i don't blame them, making games is hard enough without having to plan around a whole bunch of postgame scenarios, but i think that's an argument for leaving it out if it doesn't add to the experience
with that said, i definitely preferred speedrunning the messenger on new game+ so sometimes it can add something without adding anything!