I would liken the study of Latin to the study of a martial art. You aren't going to have many opportunities to directly use Latin, just as, unless you're foolish or unlucky, you aren't going to use marital arts directly in your daily life. The primary benefits of the study of a martial art for a modern person are in the mental and physical control it gives him, and that control is used daily. The study of Latin bestows similar benefits linguistically.
Also, like martial arts, you probably won't feel the full potential of those benefits for years until they become so ingrained in your mind that they become reflex. English vocabulary expansion is usually the driving motivation for pragmatic students of Latin, such as myself, but I would say that the greatest benefit from the study of Latin is improved grammatical control of English and thus, improved clarity of expression.
Most modern Latin textbooks are inferior to those published in the early to mid-1900s when Latin was required in public schools. In addition to the grammer rules, what is needed is emphasis on understanding the writer's intention. The passages in older Latin books are filled with footnotes because the grammar rules alone are often not sufficient to understand them. The sentences in modern books are often contrived to strictly conform with the grammar. In English, writers often deviate from the rules of grammar without risk of confusing the reader. Latin writers do this as well and actually quite often because they assume that the meaning is obvious to their Latin speaking readers, that is, they assumed that the reader is thinking like a Roman. Modern books teach this skill poorly or not at all and leave the student with a false sense of security.
Another major deficiency of modern books is their definitions. The dictionary of the book is usually tailored to the text of the book so that many possible meanings of a word, those meanings not used in the text, are omitted. A Latin word often times has 10 or more different meanings and the correct translation can only be determined from the context. There is rarely a "core" meaning for a word as many modern books suggest. A good dictionary for translation is The Bantam New College Latin & English Dictionary You may find it frustrating at first because of the large number of possibilites it offers, but as you translate more you will learn to appreciate this. It will aid you in determining the true thoughts of the writer and not just a crude suggestion of his thoughts.
The best sources for good Latin textbooks are libraries, used book
stores, and eBay. I'd recommend publication dates between 1900 and
1950. Any earlier than 1880 and the book may be in such a state
of deterioration that the acid from the pages will actually burn your
fingers. Here I am providing the full text of several books all of which are no longer under copyright. More will be added over time. I encourage you, when searching eBay, to look for books from the
30s and 40s. In my opinion, these are some of the best.