So what's the motivation to buying property you don't live in. Are they renting it out? The OP made it sound like many units are vacant. Are they buying and holding hoping to sell later for more?
Normally a boom in high-end housing is good for local trades (plumbers, electicians, carpenters, painters, decorators, etc) as the first thing most upper-tier home buyers do when they buy a place is renovate, remodel, or at least redecorate.
So these homes are vacant? From my experience in the Bay Area, these homes house their wives and small children; or their adult children. When you think about it this makes more sense than leaving them empty considering China's environment pollution.
It's possible that they are so wealthy that their income from other sources far outswamps whatever rent they would accrue from the properties, so it's not worth the inconvenience of renting them out. Remember, many of these properties are purchased outright (no loan) and held as long term investments.
Because they also flip these properties on regular basis (anywhere from 3 to 24 months) and it's significantly harder to do that with people living in.
This happens in Beijing a lot: many chinese see property as a store of value like gold or something like stock that appreciates and don't even bothering renting it out. I live in a nice beijing complex that is only around 60% full, all apartments are sold of course.
Recently it was revealed that Vancouver police actively works with Chinese secret service of some sort to track down the dirty money and send them back to China where they are promised humane treatment but as soon as they land in China they are executed.
Normally a boom in high-end housing is good for local trades (plumbers, electicians, carpenters, painters, decorators, etc) as the first thing most upper-tier home buyers do when they buy a place is renovate, remodel, or at least redecorate.