You may have built up a huge arsenal of words, but it is still important to choose the ones that best get your point across to your intended audience, whether simple or complex. The real challenge is being understood, not using awesome words, and there are plenty of circumstances where the simple words will not be sufficient for what you are trying to do.
One of the neat things about storytelling, in the verbal sense, is that, when done well, it's not just repetition of words. There are inflections, emphasis, physical gesture, posture, facial expressions, and a plethora of other nonverbal factors that go into communicating one's message. I can use words like "lugubrious" or "palliative," and by expression and action, communicate their meanings to my listeners nonverbally.
I don't think using a rich vocabulary is in diametric opposition to being understood. I think you can achieve both ends simultaneously.
