Ehh, I think the bonus chests should be both rarer and more significant. Sort of like "god's gift." Whenever we find one it should be a moment worth getting worked up over. They should contain something significant, like an ability or keyblade for me, magic for Zarco, maybe a gun for someone else or something.
Also, my vote on PVP is that it should be off. To combat that, I think the difficulty should be hard to make sure we're always on our toes.