As for whether you get an airport specific or AUS card comes down to the operational need. If your employer says you will be at more than one airport then there is usually no problem getting an AUS card. For pilots, the pilot licence is all that is needed.
As for multiple ASICs the only reason some people have them goes back to the days when the likes of Qantas had their name emblazoned at the bottom and didn't want their ground staff using them to for private flying activities. The Dept knew it happened, didn't like it, but couldn't do anything about it.