EssaySnark says, tough question to answer in a vacuum.
A 750 is a much better score than a 700. But you didn't need EssaySnark to tell you that.
EssaySnark has seen *plenty* of people get into bschool with GMATs of, like, 710. Or 690. Or 700. Or even 680. As long as the 680 score is weighted towards the quant side (and sometimes even if it's not), a put-together candidate should be in good shape for some Top 10 schools. Tougher to do Top 3 schools with a 680, but not impossible.
And all the time, we see people with 740+ GMATs not get in. (Not usually our clients.

But it happens!)
So, if EssaySnark saw a 700 along with an otherwise-strong profile, we would be feeling fairly confident.
If EssaySnark saw a 750 on a profile with big gotchas on it, we would be concerned.
That 750 could compensate for some gotchas, like a low GPA of 3.1 or so. It would not totally compensate for a horrible GPA of like 2.5. Other stuff would be needed if there were holes like that.
A lot of this depends on what school we're talking about. And what the rest of the profile looks like. EssaySnark has heard that many schools reject A LOT of their > 750 GMAT applicants. EssaySnark doesn't have hard data on why, but perhaps it's because those candidates become a little smug and think that the score is all they need.
You're heard it before: A good score doesn't guarantee you anything, but a low score can keep you out. A 700 is not a "low score" so if that's a realistic outcome for you, theoretically, you should be fine.
If you're targeting a Stanford, Wharton, Harvard -- or even an MIT or a Haas -- and you can do a 750, then yes, you should go for it, it'll make your profile that much more distinctive. Or, if you're from the perennially oversubscribed candidate pool of Asian Male, then you should also try for a higher score, since all your peers are doing that, and it could help. But you should absolutely NOT hold out for the higher score if it means it happens so late in the summer that you won't have the time you need to create fabulous essays to match that shiny score. Essays require just as much time/effort as GMAT studying - probably more - and like the GMAT, that time cannot be crammed into one weekend or two.
A 750 would be great. But a 700 should also open doors. Either way, it'll be up to you to pull off the rest of it.
EssaySnark says, take it in 13 days. Then see what you want to do. Re-testing once absolutely will not harm you, so as long as the test fee isn't a showstopper, may as well keep on the track you're on and re-evaluate after you have real results in hand in two weeks.
Good luck with it!