I usually don't disagree with YJ on principle, but when I do, I guess I have to elaborate.
Vocab is actually one of the easier things to cram for because there is a list of words (some are published in study guides and some by ETS themselves) that are frequently used. For some reasons, ETS thinks that the particular words they have chosen are inherently more important than other words. Moreover, knowing a definition is not as critical to reading anymore due to advent of the internet. I believe reading apps can now look up words for you. Does it make easier to read more books if you know Latin and Greek or just more words? Yes it does, but it isn't a critical skill. The vast majority of factual knowledge can be searched nowadays anyway. As a footnote, I do want to mention that having certain knowledge does make acquiring related knowledge much easier because our brains can make the connections stronger and more quickly, but those knowledge are usually endemic. Physicists are able to get more out of physics articles than biologists, and neither one has an advantage compared to the other when they read field-neutral research such as anthropology or epistemology (and vice versa, even though most philosophers have a bigger lexicon than the average scientist, it doesn't mean he is more able to read better).
It's more important what you read on a regular basis and what you do with that information and whether or not you are able to communicate cogently. Take Diplomacy for example. Nobody cares that a player can use big words. In fact, most of us don't use big words and we don't care when others do. It's a matter of whether the other party can understand what we are trying to convey.
Most importantly, however, is that standardized test scores are not very good predictors of how hard working one is and how successful one will be. SAT, ACT, and GRE and whatever else have relatively low correlation with success. GPA is actually a better predictor and this is regardless of what schools they are from. There is a higher correlation because you usually cannot get very good GPA unless you care and you put in some time and effort. Probably the two best indicators for success are tenacity and emotional intelligence.
For the folks still in high school, yeah, standardized tests suck and they don't mean shit, but they are one of those stupid hoops you have to jump through, so suck it up and just get it done. They only assign meanings to you if you allow them to do so. Otherwise, it's just a number or two. What you do with your life and your free time would be more indicative of how well you'll do in life.