Indeed he does. In fact, it is through the weakness of our preaching that God's power is demonstrated.
Yes, it seems necessary, but it seems to me necessary as a result of the fact that we cannot understand divine truth in its fullness. A sort of humorous (to me) representation of this is when the Children of Israel did not want to hear directly from God. They couldn't handle the truth straight on.
I agree. We do need to be careful, and not foolish, in conveying truth. But what the Scriptures say IS what it means —it is WE who can't see it as such, and so need it explained. And that, by others who still fall short in understanding to the full.
I tend to think that God has weak humans to preach to weak humans, weakly, because his truth will not otherwise be understood even weakly. If I tell my neighbor that what the Bible means by such and such a verse is that God is omnipotent, he may understand that better than to simply read the passage. That does not, however, mean that he understands what is necessarily implied by "omnipotent".