Granite Falls could really benefit from having a swimmable lake with row boats to go fishing in, but that would require a major work over for that world which I feel is bigger than "refreshing".
Making the world livable would be great for more rustic games and I'd love to have that choice. If that's not possible for some reason, I'd love for them to allow bugs to spawn in all worlds. I use a mod for that now, but it'd be great to see it added to the game.
I'd also love to see more pack specific sentiments added to all of the older packs including Outdoor Retreat, as well as more traits and aspirations.