[Imladris]

As far as I can tell, it's perfectly logical to assume that a wizard can communicate with a moth (now, I don't know if Gandalf could do it since I haven't read all of Tolkien works, but I'm talking strictly movies here). The fact still remains that they would have had to introdcue another character that would not appear in the films again. That costs time, money, and a potential lull that could possible bore viewers (remember a book is different that a film). A theatrical release can't be as long as a director jolly well wants it to be. There has to be a limit. If he had put Radagast in there his screen time might have taken time away from a more important part of the story.

And yes, you're right. Radagast was influential. But we still got Gandalf there with a plausible reason. Or would you have preferred PJ to go through the back story about why Gandalf wouldn't trust the head of his order and that's why he didn't go to him immediately but had to be sent there by Radagast? Actually, if you read the part in FotR again, Radagast had just come to warn Gandalf about the Nazgul and that if he wished aide to go to Saruman....

The way PJ did it, he killed two birds with one stone.

However, I can tell that this argument could run in circles so this shall be my last post on the subject.