As far as I am aware you are only allowed to wear it when you have a 'legal' reason to be in that area for the requirement to have an ASIC. IE you don't have to wear one in the terminal if your not operational crew, so you don't need it. To get the discount in the terminal simply show it out of your pocket before ordering, I would not be wearing it around in customs controlled areas without a valid reason! Duty free in BN at least has a 10% discount for the ASIC, but gives 20% if 'operational crew', used to give the latter to everyone but obviously was impacting too much when everyone with an ASIC was using it!
The airlines consider them 'valid' ID in terms of identification, so certainly does not hurt in showing it to ID yourself for checkin, and may help with getting an emerg exit. Keg esp if you were in uniform, Virgin does seem to like to put especially Cabin and Tech Crew in emergency exits, simply for the basis of their EP training and backgrounds, which makes sense from a safety perspective.