I Corinthians 2:4

And my speech and my preaching was not with enticing words of man's wisdom, but in demonstration of the Spirit and of power (KJV)

Then: A clear gospel and a clear presentation go together (Baker, p. 47). The Corinthians would have no space to complain "they couldn't understand it." There are no "bait-and-switch" tactics in Paul's preaching. Rather it is all wysiwyg - What you see is what you get. Think through the various groups in Corinthian society - poor, slaves, freedmen (business class), government workers, philosophers and aristocrats. (Ramsay, p. 29-30). Paul needed everyone to understand the message. That's a basic reason to skip the smooth oratory. No one would leave thinking they'd heard a great speaker, but didn't understand points in the argument. Remembering Paul's classical training in the law, this is more probable than beliefs that Paul lacked the skill to match "words" with the sophists (Ramsey, p. 24).

Now: Go to school for years, become academically capable, and then discard your skills for the sake of listeners. That doesn't sound like a sensible approach. Yet great teachers of today are still able to do that for the sake of the cross, for their love of Christ, and for their love of the lost sheep. Paul did use quotations, vivid images, metaphors, contrasting ideas and rhetorical forms to illustrate his points. May all who are called pay attention to Paul.

Extra Source: Cornerstone Biblical Commentary 1 Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.
Historical Commentary on First Corinthians by William M. Ramsay, ed. by Mark W. Wilson, Kregel Publications, c 1996. online at http://books.google.com/books?id=J7RyILzCn8UC&dq=Ramsay+Corinthians&printsec=frontcover&source=bl&ots=dwdPJmUUh6&sig=G9Pe1_oY5izKuYc4bC9gnVjRdds&hl=en&ei=6SYdS665B5Tl8QaI4dHeAw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CBQQ6AEwBTgK#v=onepage&q=&f=false