I think it is generally true the more recent the colonial period the less preservation of colonial buildings you will see. Another factor is how long the colonial period lasted. For nearly all of Latin America the colonial period lasted around 300 years! During 300 years there will be quite a bit of "fushion" between the indigneous and colonial cultures or in some cases "cultural genocide". Furthermore, no one remembers their homeland before the Spanish arrived or even for that matter their nation not being independent from the Spanish.
In Asia it is very different. People in China and Korea remember what the Japanese and the West did. Japan colonized Korea for 35 years, in which tremendous hardship and suffering occurred. (In many ways Korea under Japanese rule was very similar to various forms of European colonization, but the difference is no one is alive to remember the Spanish in the 16th century or the British in the 19th century) Japan also sought to eradicate much of Korea's culture and traditions (following the example of European colonizers). Korean language was eventually banned in favor of Japanese being taught in all schools.
Moving to China, during the chaotic period following the Opium Wars all the way to WWII, China was being torn apart by 8 countries trying to colonize different portions of the country. The British, Germans, Japanese, Italians, Russians, Americans, and the Austria-Hungarians made an alliance around the year 1900 in order to put down the Boxer rebellion and subdue the Qing government. (Yes, the Japanese, British, and Americans were working together to plunder China) The fact that the Europeans and Americans sought to carve up China like a melon is not lost even on todays generation. It is no wonder the only "colonial" WHS in China is the Historic centre of Macao, which was a center of trade, and in no way were the Portuguese able to dictate terms with the late Ming or early Qing dynasty.
In countries such as Korea and China, the "foreigners" were kicked out and a strong period of nationalism followed. It is perhaps revealing that China is considering nominating the death camp/human experiment lab Unit 731 near Harbin where the Japanese committed the most unspeakable atrocities as a world heritage site in the coming years. Indeed, as I mentioned before many Japanese buildings in Korea have been destoryed with great fanfare, and in 1 or 2 cases it was broadcast nationally. Nevertheless, there are important buildings and monuments remainging in China, Korea, and Taiwan from the Japanese colonial period, some have been preserved. However, I cannot imagine any of them (except a small possibilty of Taiwan) ever being nominated as a world heritage site in our lifetime. Perhaps in 100 years if any of these sites still exist.
http://en.wikipedia.org/wiki/Unit_731