One of my favorite vocabulary-builders is Merriam-Webster’s. It is a green paper-back that has quite a few pages, but I cannot find a vocabulary-builder that is as readable as this one. It introduces each entry word with its roots and origins. Some entries contain Greek myths, and others tell us background stories. (I forgot details because I read the book as soon as it was piblished.)
Using a vocabulary-builder is a rather streamlined way of learning English, but as far as this book is concerned, it cannot meet your expectation. You will end up spending a lot longer time on the same one word than you would if you read a different, more efficient vocabulary-builder.
Again, as is often the case, there seems to be a trade-off. If you spend more time on one word, you will be able to understand the word more deeply, and thus the word will be better stored in your brain. The downside, however, is the number of words that can be learned that way.
Merriam-Webster, therefore, is not a strong recommendation for TOEFL learners, but when they have reached the required score, it should always be on the top of the list. I would say that it is the most luxurious pleasure to spend an unnecessarily long period of time on just one word!