I think you're going wayyyy too overboard with the vocabulary. Just let new vocabulary come to you naturally, not forced upon you. In saying this, complex vocabulary is NOT favoured over complex ideas. I think you're too concerned about your essays sounding good, but not actually being good.
Before you tackle any essay, make sure you plan it out. Underline the key words, find synonyms of these words, ask questions of the question, come up with 3 or 4 key ideas, write out the topic sentences and trust me, you'll feel far more confident writing the essay.
Your essays are lacking depth because you haven't studied your texts deeply enough. Delve deeply into your texts and use abstract evidence as well. Make sure you develop your own unique interpretations of your texts.
Then again, I don't know what your writing is like. I suggest you do what Rohitpi said, and join the essay forum!