What do you mean by "treasures"? Do you mean the same random stuff that you collected in Pikmin 2? Those were "treasures".
The variety of collectables in Pikmin 2 was really cool, but I don't think that they would or should do the same thing again. I've mentioned in other threads my idea of collecting fossils or bones to assemble complete skeletons of larger creatures such as cats, mice, fish, etc that Olimar has not encountered alive.
Or maybe you need to find ingredients for new sprays and medicines. Some of them could come from plants and some could come from creatures (mostly bosses, I guess).