Hi,
Most universities ask for GRE. I would say it is totally necessary and worth studying for, especially as many students do present a competitive GRE score and you want to stand out. The GPA and other experience are already done, now one thing you can do to add point is GRE. It is not something extra hard, though you need to plan some time to study for it. Advice:
1. Good online course: Magoosh
2. You might want to leave enough time to do 2 attempts - to make sure you are satisfied with your final score.
I am organizing a meetup event on 14th August, this Sunday in Manhattan. I will share advice about GRE math, come by if you're around: http://newyork.craigslist.org/mnh/lss/5722106731.html
good luck!