Eloquence in Preaching

In the book, The Power of Words and the Wonder of God, John Piper makes the case for eloquence in preaching.  While the apostle Paul decried a certain kind of self-promoting eloquence (1 Cor 2:4), Piper makes the case that eloquence can be redeemed, and used to preach the Gospel with power and clarity.  He lists five keys for doing so:

1)  Keep Interest:  Use artistic, surprising, and provocative language.  This won't save your listener's soul, but it may keep him awake to hear the Word, which can save his soul.

2)  Gain Sympathy:  This does not mean telling sob stories but, rather, relating to your audience in such a way to earn their respect, attraction, interest, and concentration.

3)  Awaken Sensitivity:  If a poetic phrase can cause people to notice the magnificence of the sun, their next step might be to see that the heavens are telling the story of God.

4)  Speak Memorably:  Cadence, parallelism, meter, rhyme, assonance, and consonance are tools that can increase the impact of the message by making it easier to remember.  (Could we add alliteration to this list?)

5)  Increase Power:  When eloquence and truth combine, it makes for powerful words.  Indeed, anything less does the truth an injustice.

Of course, Piper stresses that all of the above are in vain unless the Spirit blesses our preaching.  What do you think?  Should a preacher intentionally strive to be eloquent?  Or could this be considered a form of manipulation?