Got feedback today - it was the "there's nothing specific to work on feedback" which I basically just means I just wasn't quite as impressive as some other applicants. Oh well, at least there weren't any glaring weaknesses in my profile.

They're pretty transparent about it - they flat out say that they don't review applicants in subsequent rounds. More than likely (since they're a small school) they'll have an idea of what their capacity is after the Nov/Jan deposit deadline of April 26. Even then, they might not look at the waitlist until late May after they release April Round decisions.

Take the exam. If you score above 710, send it to them, if not, don't send it. The only way they would find out about a lower score is if you re-apply next year.
Just one thought though: I know the application process in holistic, and you must present your strenghts in all aspects possible, but it just sounds weird to me that someone with a 710 receives such a feedback, and people with lower scores don't. As I said, they look at all aspects of your profile, but if the comment is related to your GMAT, than people with similar or lower scores should receive the same feedback. And a 710 is now not a good enough score? Are you serious? A 10 point difference to a 720 would make you a better student just because you are above their average? I'm sorry, I can't agree with something like that....
To me, this feedback is being based on the personal opinion of the one who reads your file in 20 minutes just to write your feedback. I cannot believe it is derived from the group decision the committee made about your file. To tell you the truth, I wouldn't need an official feedback to know that a 710 could be better. But it is 7 points below their average, so it's totally acceptable. They should tell you what really kept you out for the moment, the 710 just can't be it.
Sorry for the long post, but it's so unfair to be waitlisted, expect a decent feedback, and receive a couple of sentences that don't help at all!