UI elements should have haptic feedback
As a user, I would like to have button presses have some non-visual feedback as well as visual. The button is often hidden by the finger when it is pressed, so it would help to have it "click" as well as highlight.
Same for most of the other widgets: ComboBoxes could have the same feedback of the PullDown menu, sliders could have some sort of low-level buzz as long as the user interacts with them and so on.