You don't need to complete an entire graduate degree to show them an "improved" GPA, but sure it'll help. At a minimum, take a few classes.
If you do a "filler" program, are you intent on staying in SF even then? Because I don't believe you can get into the Stanford or Haas MBA program with or without additional coursework alone. Another "top" MBA program....... maybe, depends on your definition of top.
2.7 GPA, 680-700 GMAT, and 2.5 years as a commercial bank analyst are all working against you. It's all below-average or average.
Focus on what you can change.
1) Kill the GMAT, now, while you can. Spend every available moment studying for it. Do not settle for 680-700.
2) Take your additional coursework and ace it.
3) Find some non-profit or other ECs (maybe school clubs) to get involved with in a leadership capacity.
4) See if you can take on some leadership role at your work. Lead a project, come up with some innovative ideas and ask if you can try implementing them, you need a leadership "gold star" from work.
2.7 GPA, 750 GMAT, President/Organizer/Founder of Clothes for Kids, 4.0 in 18 hours of recent graduate-level, quantitative coursework, and you successfully lead and implemented a few new programs at work. Now you seem very marketable for a top MBA program.
EDIT: Forgot that Berkeley offers Evening and Weekend MBA programs. I don't know the stats, but PT programs are usually less selective than their FT counterparts. I would take a Berkeley PT MBA over any of the other programs you've mentioned.
ME: PROFILE | CPA: BEC AUD FAR REG | CMA: ONE TWO
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