No - I don't think you should take the GMAT again.
Your GMAT score is just a formality or a box the Adcom ticks away to evaluate whether you will be able to cope with the course work at school. Secondly, you wouldn't have received an interview from a top 4 school if the school had any doubts about your ability to excel at school. Plus, you're from a very diverse background and have a somewhat unique work experience in Africa, Australia, and Asia that helps distinguish you from the crowd. In my opinion you need to focus more on targeting the right message in your essays and executing it flawlessly rather than taking the GMAT.
How was your interview? Could it be that there was no cohesion between your essays and your interview? One has to really nail almost every aspect of the interview with a top 4 schools.