Using new words does not necessarily mean using pompous words.
You can understand the notion of "new words" in more than one way. For instance, language keeps adding words for new objects or activities that we did not name before for the simple reason that they did not exist. Examples of this are "texting" and "freemium", a condensation of "free" and "premium" used in business to express that a basic product is free while additional, related services are charged. The reason why we cannot speak in dead languages such as Latin is that they lack many of the words we now need for factual communication.
You can also think of "new words" in relative terms. Words that are new to some may be familiar to others. This depends on the extent to which a speaker of a language has built up his/her vocabulary. Learning new words enlarges the scope of comprehension. These words may be retained in memory as passive knowledge -that is to say, you remember their meaning when you hear or read them- or may be activated; i.e. you may appropriate them and use them.
A poor vocabulary yields limited thought, for our thinking processes rely on words. So by all means try to learn words that are new to you, always bearing in mind that registers (styles of language) do not mix kindly. We do not use the same words in a colloquial exchange, an academic paper, and a literary piece.