Hi ashie, if you want a career in PWM, then it is quite hard to get in unless you already have a good network in the country where you operate. A MBA or MSc does not make a difference really for PWM.
As for trading, it depends how technical you want to become as a trader. If you trade plain vanilla things, an MBA should be fine. If you trade exotic instruments, some detailed knowledge about financial engineering might be needed. In that case, an MSc. would be the way. A good substitute for an MBA, and a one year program, the Masters in Finance MiF from LBS could be a good alternative if the UK could be a potential area of work for you.
Depending on what kind of schools you are targeting, the GMAT will vary. Are you looking at a top tier school? If so, and depending on your GPA and work experience, something higher than 670 would do you favor. Otherwise, for a lower tier school, anything higher than 600 should allow you to go to a decent school.