When you go from T1 to gates 13-21, there is a new Sky Deck for plane spotting, you can spend some time there and get to know the airport expansion plan.
HKG has yet to return to its former glory and not many shops are in operation. I am not sure if there is any 24-hour option. On the other hand, in the terminal air-side area you will see some new games/booths for passengers to kill time waiting for their flight.
But the best option is still entering Hong Kong and get a proper hotel room. Regal airport hotel has provided me with bad service before so it is on my personal black list. But it should be a decent enough hotel.