Although I don't know much about Caiques except the basics of the species, I know that whether a healthy bird goes to the bottom of the cage or not, has a lot to do with species. I do always see Caiques at the bird store rolling around playing on their backs. Some strictly arboreal parrots are always "up" in the trees, and it would be out of their natural comfort zone to come down where predators may be. On the other hand, some parrot species naturally spend a great deal of time on the ground.
I actually encouraged my Pionus to "use" the bottom area of his cage, since his old cage (as well as his new one) are deep vertically, and I didn't want everything just up top and all the rest of the space wasted, I put toys down low, and one thing he absolutely loves is his big toy box on the cage bottom full of foot toys! It's funny to see him going through the toy box and picking a toy, dropping it (or sometimes putting it back) and getting a different one, etc.
