I always find it awkward to compare city-states to regular-sized countries. There is no “rural Singapore.” A lot of these independent cities are tiny because they were rich and powerful to begin with; That’s a fantastic starting point that no other country can have.
There’s not much many other countries can learn from Singapore because they all either don’t have enough money or have a greater variety of people to convince.
You seem to be conflating rich and poor and rural and urban, which have very little relation. Singapore was very poor, baring some rich businessmen, mostly Chinese IIRC, and had ethic tensions to boot between the Chinese, Malay and Indian populations it had ( one of the main reasons it was expelled from Malaysia).
New York was also very poor, barring some rich businessmen. You have to look at it relatively to its surrounding. Of course there were poor people too, but they lived in the “suburbs”, not in the middle of deserts like, say, in the US.
If I remember correctly from my visits in SG then the country was not rich from "the beginning", in fact it was very underdeveloped until the late 60s and beginning of the 70s and it worked out for them because of it was a dictatorship under Lee Kuan Yew and made the right decisions... and was tolerated by the West at the same time.
Underdeveloped by whose standard? An underdeveloped city does not seek independence. You have to place it in its context. It probably was not the poorest city by a long shot even at its birth.
There’s not much many other countries can learn from Singapore because they all either don’t have enough money or have a greater variety of people to convince.