Hi corridormethod,
To start, Business Schools generally do not care whether you retake the GMAT or not, so there's no inherent harm in doing so. That having been said, I've never been a fan of creating a plan that is based on taking the GMAT twice on purpose - that type of thinking implies that you might not work hard enough for your 'first' attempt (and THAT would be a waste of both time and money).
Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) What were your Quant and Verbal Scaled Scores for your 640?
2) What type of studying have you done over the last few months?
3) What study materials do you currently have access to?
4) Have you taken any practice CATs/mocks recently? How have you scored on EACH of your CATs (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
5) What are the exact application deadlines for the Programs that you plan to apply to?
6) How do you know that you "need" a 700+. What if you scored 690 - would you still apply?
GMAT assassins aren't born, they're made,
Rich