Andrew66, you have full access to the Terminal with as large a range of shops as you could require. I recall that you do have to go through Security after disembarkation en route to the Departures area. If you have Lounge Access, depending on status, you can also park yourself in the BA Lounge which is in the process of reinvention at present (see other posts on this Forum). It all really depends on your available time and priorities – mine with that sort of break is a stiff walk in order to get the circulation going and there is plenty of opportunity for that at Changi too!!