I like Joakim Noah, but I don't think he's the guy we need, not at this point in his career.
The Celts lack a standout paint defender, yes, but more than anything they struggle to score.
Joakim Noah is in a similar stage of his career as Andrew Bogut, now. He's a designated hitter. Keeps the ball moving and extends possessions sometimes on offense, and he can mostly finish open looks in the paint. But he's not going to really help your team score. He's all defense and rebounding.
What the Celtics need is more two-way players, not to add another guy who only helps on one side of the floor.