Caron Butler is one of my favourite players, but trading for Allen or Pierce for him? Noooo way.
First of all, Butler is not as young as you make him sound like. He's 28, will be 29 in march. So he's only a few years younger than Paul and Ray. So if the Celtics were going for him, it wouldn't be for the future, the post "Big Three" era. Because when they go down, so does he (more or less).
Secondly, I doubt the Wizards will trade away Butler, for the reasons you've pointed out. He's without any doubt their best player right now. Gilbert Arenas is, as someone wrote, a pest, while Jamison just isn't a threat when facing the top PFs in the league. I think the Wizards will try to deal Jamison first and then build around Arenas and Butler (or trade Arenas and rebuild)..