Man you must be out of your mind . 700 is damm good score and your wasting it by applying to NUS . Haven't you seen the sites of universities in the US , the average GMAT score ,barring the top 7-8 universities ,of students their is around 640 -680 .

I would advice you to

1) Wake up to the technology revolution and go and get these information .
a)Average Expected score
b)Minimum months of experience required for all universities.
From the sites .
There's a list of top MBA colleges in the world and in US published by Forbes which would be a good starting point.
2) Look at few of the universities in Europe , they have a world standing and are pretty good.
3) Concentrate on your Essays and Reco ( If you lack there then you are in trouble ) .

Man GMAT is not the end it is only a means to an end . And if you have not done any social work in the past few years it may be a good thing to do it now and mention it in your resume .

But if you still wanna go for NUS NTU well be my guest , your score is good enough and experience more than sufficient ( If after your MBA you are considering a change of field , there is no point gaining more experience in software industry )

All the best