How useful is skyscrapers and high buildings lighting to get a visual reference for pilots by night? (not obstruction lights, just general lights)
Buildings and their lights can be very useful to aircraft in VFR conditions at night to orient themselves regardless of the type of aircraft.

Three building lighting examples that I often used were:


When flying Metroliners for a commuter airline that operated to Walla Walla, WA, I would call for a visual approach to the airport when I saw the Washington State Penitentiary. It's distinctive pattern of bright lights, especially those around its perimeter, made it stick out like a sore thumb.
When flying night freight in 727s, from many miles out, we could see the blue neon lighting outlining the Sofitel Hotel just across the road from the southwest corner of Miami International Airport.
Back in the late 1990s, the high rise hotels along the beach at Tel Aviv had a distinctive pattern. Head just to the south of them and you were lined up for Ben Gurion airport when approaching from the west.


Really, if you go into most urban airports regularly at night, you learn to recognize the pattern of the lights and can use them to orient yourself.

Freeways with heavy traffic are also helpful. Interstate 5 running south from Albany, OR to Eugene, OR has a 33 mile straight stretch that produces a line of headlights. Aircraft approaching from the north can aim about 15&deg; right of that line and be headed to the Eugene Airport.