I think there's a bit of everything. I did see some footage where she was following a yellow bird to an upgrade spot. BUT they seem to have focused on variations now for all side objectives so it doesn't get dull and repetitious. One example a reviewer mentioned was when you get to one of the hot springs, you find a bunch of naked men in the pool and when they recognize you, they freak the fuck out and run away. Little things like that throughout that make them worth finding, aside from the gameplay perks.