Actually, applying for PR for your vietnamese wife is not at all that difficult. There have been a lot of guessing and a lot of speculation. But all comes down to some simple logic and requirements:
(1) You and your wife should not be black listed by government in any way. eg. no criminal record etc
(2) You should have some education and a stable job. You should be in this job for minimum 2 to 3 years. Pay wise should be reasonable and stable. For example, there are some bros earning $1800 a month but still can get pass this requirements. Government look at annual pay, inclusive of bonuses. Some may earn only $1800 a month, but still got 13th month and another 3 months of bonus. So 1 year, that bro is actually earning $1800 x 16 = $28800.
But one thing is for sure is that the more highly educated you are, the higher your pay is and the longer you stay in the same job, the higher will be your chances of getting PR for your wife.
(3) Your chances will be much higher if you are paying income tax and has been contributing to CPF. I know of a bro who is earning $5500 a month but yet cannot get PR for his wife as he has been evading tax for the past 2 years.
(4) The marriage should look normal to the government. What this means is that the marriage shouldn't arouse suspicion from the government that its a fake marriage.
Its not that tough and neither that easy. There's no need to feel bad even if your ba xa cannot get PR at the first instance. Try to improve yourself the following few years.