You need to “speak” naturally and well in language appropriate for your target audience. I don’t know what you’re trying to do with your difficult word strategy but if you’re trying to impress someone, forget it. It will show and un-impress very fast. The goal of writing, as I understand it, is to communicate ideas clearly and well. Hiding good ideas behind difficult words sort of defeats the purpose, don’t you think? Then again, if you’re writing articles for PhD’s they will expect you to use language appropriate for the topic—they don’t want to read grade school language. But if you’re writing for the general public, stick to vocabulary the general public understands. If a difficult word is necessary to the article or story, explain it.