Lily Bracegirdle, re Book vs Flim Faramir, I have the book open right here:
"Then all were silent, but at length Faramir said, 'I do not oppose your will, sire. Since you are robbed of Boromir, I will go and do what I can in his stead - if you command it.'
'I do so,' said Denethor.
'Then farewell!' said Faramir.'But if I should return, think better of me!'
'That depends on the manner of your return,' said Denethor."
As I recall, the film equivalent of this scene was reproduced almost word for word. The main difference is that two scenes were reduced to one, which was fair enough. In the novel, as in the film, Faramir says this soon after his father has told him off for having some initiative and then, incongruously, accused him of being Gandalf's stooge. Now, I'm not saying he goes on the mission so that his father will love him - I think you're right there - but it's certainly in his mind : "What can I do to prove myself to him? Nothing's good enough!"
An interesting post in general, but I thought perhaps you might have forgotten this scene actually was in the novel as well as the film.