Are you planning on applying to start school this fall or in fall 2012? If you're looking at R3 deadlines for this year, it's probably too late to make huge improvements. If you're looking forward to the next go-round of R1 and R2 deadlines, I would recommend studying some more over the next 3-4 months then taking a summer GMAT to set you up for applying in the fall.
I was in a somewhat similar situation to yours--when I took the GMAT in late August my Q46 (75%) was significantly lower than I expected based on my
MGMAT exams, which led me to believe I'd made some dumb mistakes that I could have fixed on a second GMAT. Based on the advice I got from several Haas and Stanford students, I decided not to take it again and instead put my time into my essays for R1 deadlines. I got a little worried when the adcom member at a Haas info session said they preferred students with at least 80% on quant, so I guess the fact that I got good grades in my undergrad quant courses (calculus, stat, engineering, physics, chem, etc.) was enough to prove to them I could handle quant material.
Then again it all depends on what schools you're looking at. A 700 may be perfectly fine if you want to go to a top 20 as opposed to a top 10 school, or if the rest of your profile is very strong.