The GRE is? That's a test I might end up taking as well.
But on the GMAT, having a strong vocab doesn't really help much? Or actually in my case, having a weak vocab doesn't really hurt too much?
Well don't quote me on the GRE thing, but I believe it is. On the GMAT, a strong vocabulary won't help you. I took a practice test yesterday and I can't really think of one word that any normal college student wouldn't have known. GMAT "advanced" words are things like "significance," "acquire," "presuppose," "deleterious," or "endeavor." While you're reading, it doesn't even register that a word is difficult. I guess "deleterious" might be a somewhat more advanced word, but reading it in context would help you figure out the meaning even if you didn't know it.
I remember SAT "advanced" words were words you had never seen in your entire life outside of the test like polyglot, august (not the month), natatorium, shibboleth, or whatever. You don't need to know these.
My previous list is representative of advanced GMAT words. Trust me, strong vocab won't help much.