Do a lot of rich people move to Vietnam?  

There are rich people all over Saigon. Every homeowner who has a house in the epicenter of Saigon is pretty much a millionaire.

Many foreigners retire in Vietnam because the living expenses are low. Someone living off social security benefits of $2000 a month will struggle in the US, but if they live in VN, they can live comfortably. Also, foreigners in VN who work as english teachers get a higher salary than the other developed Asian countries like Japan, Korea or Taiwan. It makes sense to live in Vietnam and work there. You have your choice of moving to a developed country like Japan to work and live, but the work schedule will be hectic and living expenses high. You will get job burnout.

I know an english teacher in Vietnam making $2200 a month and living expense are $800. She saves $1400 every month. She used to work as an english teacher living in Taiwan, making $1800 a month but living expenses were $1400. Even though Taiwan is more modern and has good public transportation, she told me living in Vietnam changed her life for the better.