I do use the wing anti-ice on the 320 as, well, anti-ice. In conditions which seem likely to me to be conducive to the ice accretion (-20c to 0c in high moisture concentration) I select it before waiting for a buildup. Having flown turboprops for years I have a healthy suspicion of ice anywhere on an aircraft. My company don't have detectors and we still use the original method described by the OP for the engine AI. Seems to work just fine.