There are certain collections specific to a world that might be a little easier. Like the snowglobes, as Kathykins mentioned, and also posters can only be found in San Myshuno, I think. Those are relatively easy to find. Then Sulani has the shell and treasure collections, although the volcanic lot traits does help with the crystal, metal and fossil collections. Frog, insect and feather collections are fairly small and probably won't take as long to complete, and pets will help find feathers, at least cats do...not sure about dogs.