I am currently travelling around China, I have been to Yunnan, Sichuan, Hunan and now Jiangsu. One question that keeps coming to mind that I cannot find an answer to is; why have some of these cultural relics such as the Beisi Pagodain Suzhou not been completely destroyed? Did the red guards use these locations strategically or just did not get around to destroying them?
While the Chinese Red Guard did attempt to destroy and replace the "Four Olds" (ie: Old Customs, Old Culture, Old Habits, and Old Ideas), the PRC government stopped short of endorsing the physical destruction of products. In fact, the PRC protected significant archaeological discoveries made during the Cultural Revolution; such as the Mawangdui and the Terracotta Army.
That said, many enthusiastic Red Guard did destroy numerous statues and architecture, but anecdotally, alot of the destruction was limited by high ranking members of the Communist party. For instance, Zhou Enlai (who was the Premier then) saved the Forbidden City by closing the gates and deploying the PLA against the marauding Red Guard.