Hi to the original poster!
Thanks for posting. So with your 670 GMAT, I wouldn't say you are 'out of the running' per se at schools like Tepper, just based on that (GMAT range 620-750 for middle 80%, fyi).... BUT bumping up that score would definitely help, and given that your profile at this point sounds pretty similar to so many Indian IT applicants, then yes it would become more important. Additionally if this was your first time taking it, it's not a bad idea to try again; schools take the highest score and taking it twice or more is not uncommon. And if you were scoring better on your practice tests, that shows me that you are likely able to score higher.
I will also point out that JUST getting a higher GMAT score won't be all you need to do; MBA admission is based on a holistic view of YOU as an applicant, and once you have the quantitative factors down (grades, GMAT, etc), the focus is then on the more personal factors... who ARE you? What key experiences have you had in the past? What will you bring to the program that others will not? Why do you need the MBA? How do you envision your career? And so on. You'll need to work extra hard to show how you are different from other IT applicants.
Hope that is helpful, let us know if you have additional questions. Good luck!
Thanks a lot for your reply! I plan to apply for NUS and Nanyang and at the same time prepare for another attempt within 2 months. Will this idea workout?