I could not recommend the idea of foregoing a hotel for the CX lounges
I was on CX844 recently and stayed in the Pier until closing at 00:30. For the final 2 hours I napped in the sleeping area/quiet zone
Then went over to The Wing. At about 1am everything started to shut down and get cleared away. Most pax were just waiting for 844 to board. People in a zombie like state just wanting to get going (and to bed on the aircraft). Our flight was late, departed at 02:30am so it really was an endurance test just waiting waiting waiting. I love CX lounges and think The Pier might be my favorite J lounge in the world, but its a real slog killing the hours between midnight and 5am at HKG
Maybe the Plaza Premium that stays open al night is better, but maybe that just means you drink too much, unless there is some sort of daybeds that you can lie down on