Here's what I ended up doing. Had to rush even more to avoid closing times, since my flight arrived at 9:00pm (an hour late) and I took taxis instead of public transportation in some cases, even when public transport was available.

1. Airport express to Kowloon Station
2. Explored Temple Street night market
3. MTR to Tsim Sha Tsui
4. Walked through Peninsula Hotel, listened to some big band music performing for a bit
5. Caught one of the last Star Ferries of the night, then taxi to Peak Tram Station
6. Caught the last Peak Tram at midnight (only 2 other people on the Tram - at busy times, there can be more than an hour wait)
7. Admired night sky and harbor from Victoria Peak. Stayed for a while, since I had decided not to come back again at sunrise.
8. Taxi to Wan Chai, walked around Lee Tung Avenue
9. Watched the crowd at several famous nightclubs for a bit (Ophelia, Dust 'till Dawn, Joe Banana), just to say I'd been in them, but didn't stay long. Got a kick of the signs offering discounts to airline crew. Hoped I wouldn't run into the flight crew for my flight that day.
10. Walked through Admiralty district, then Central district, where I went under the HSBC tower and looked at the exhibits detailing Hong Kong's history. Made sure to rub the paws of the HSBC lions (Stephen and Stitt).
11. Walked through Lan Kwai Fong - Wyndham Street, Hollywood Road, and Pottinger Street
12. Breakfast at 24-hour Flying Pan restaurant (great pancakes, free WiFi, no pressure to leave).
​​​13. First train back to Airport

There are many better layover options if you're there during the day (unless you really do want to do some clubbing), but as I had no choice, I did a rushed, but still very enjoyable walking/riding tour.