I don't know, it just seems like what God has to say would make more of an impact if it came from someone "perfect."
People aren't going to believe anything someone says, if they're so imperfect, like you say. Pat Robertson says he speaks for God, then he talks about assassinating Presidents of countries and murdering homosexuals.
If God was going to use someone to truly speak for Him, then they're going to be HAVE to be perfect to actually be believed. You really think he'd choose someone with so many character flaws that are easy to exploit, like a druggie or a murderer, instead of someone perfect like Jesus? That wouldn't make any sense.
The reason that Jesus is revered the way he is now is BECAUSE he was perfect, and because he was perfect people believed that he actually spoke for God. There was nobody before him, and nobody after him, that has had such an impact, because everyone else is just a regular person.
Christianity would probably be just another footnote in the History books if God had used Average Joe instead of Jesus. If He truly wanted to make an impact like that again, he would do the same thing He did before.