Try this test. Is your English is really good?
English is way more rich than the spoken slang, with all kinds of nuances and rare words you're not necesserily use everyday, ever changing to meet the needs of the modern world and with a rich cultural history.
If you learn English well, you have not only brilliant SAT score, but also access to one of the biggest and brightest bodies of literature that has ever existed, as well as to the many new examples of its power, as in films and song lyrics.
Memorizing English words is one activity where you can be sure you will never be wasting your time.