In 1989, URA drew up the Conservation Plan mapping out the criteria and methods for conservation. The bulk of conservation areas today are in the Central Area. These were early ethnic settlements.
Details matter in conservation.
While saving an individual building may serve to show a certain architectural style, what we want to do is retain the ambience of an area. This requires conservation of whole areas like Chinatown. This critical mass of conserved buildings also creates visual contrast and excitement within the city.