86213:
I actually think you can do both because it comes down to a matter of timing.
First, you should throw in a bunch of applications to safer schools. Even if you improve your GMAT score (and that's an IF, right?), you might not get off the waitlist. Unless you received direct feedback from these schools that that is the missing ingredient, you are not guaranteeing yourself anything.
After you submit those applications, you should push to retake the GMAT. These waitlist decisions move very slowly and sometimes even get pushed back until near the end or after R2 decisions. If you do better on the GMAT, you should submit that score (along with any other relevant updates) to the schools for hopefully a "second" look.
Hopefully that does the trick! Best of luck.