Have you tried Spike before?
If so, and you know what to expect, I say use it. I've taken it for study sessions and prior to tests (although none as major as a GRE) with nothing but positive experiences.
I never felt overly-stimulated or anxious at all (although I'm not one prone to test anxiety).
If you've used Spike before, I don't really see how it would hurt. I think it would help your mental clarity, but I wouldn't wait till the day of to test drive it.
Hope you can pull something out of this (and good luck on the test!).