Christie's Asian art sales in Hong Kong sent records tumbling. One reason is the new buying power of Mainland Chinese such as Shanghai-based Wang Wei, who has spent more than 1 billion yuan ($146 million) this year with her stock-investor husband, Liu Yiqian. The couple paid HK$7.2 million for a vivid work by Liu Ye, titled “I Always Wanted to be a Sailor,” and they spent about 170 million yuan ($25 million) at Beijing’s Poly International for a Ming Dynasty scroll by Wu Bin, the highest auction price ever for a Chinese painting...