Characters and imagination

Partly because a new movie about Brideshead revisited is about to be released, and partly because there is continuing interest in the book, a new book on the inspiration behind Brideshead has been published -- Madresfield:The real Brideshead by Jane Mulvagh. Having reading an excerpt from the Saturday Telegraph Magazine, I am sure the book will interest those people who are intrigued by such things, but it does also further debate on how much is in the author's imagination and how much does an author pick up from those around him.
The Lygon family certainly had a huge impact on Waugh. He used the setting of their house, Madresfield in several of his books, including Brideshead Revisited and A Handful of Dust. The Lygons were approached but refused to have the 970s tv series of Brideshead filmed at Madresfield. Waugh also wrote to one of the Lygons to explain that the characters might be seen to be certain members of the family but they were not. Certainly similarities could be drawn, but he wanted it to seem to be a product of his imagination.
Until I read the article I had not realised how much Waugh had drawn from the Lygons and others in his circle. I assumed that most of the situations etc had come from the melting pot of his own mind. But does it matter? As surely the characters he created were his wherever he got the inspiration?
As a writer, my characters are not really based on anyone. This is why I use things like Jung, Myer Briggs, archetypes, ennegrams, astrology, birth order and a number of other pop pysch methods to try to get to the core of a character. And I used research as a jumping off point, but I do try to imagine my own meals and my own decor. What would my characters notice is a far more important question rather than what would I notice or what should I be trying to faithfully describe...
My problem with trying to base a character on someone is that my perception of that person would come to the fore rather than the character I was trying to create. I think it does say something for Waugh that he was able to move his characters about while closely basing them on certain people. However, perhaps it is easier to do if you are writing a contemporary, and bit harder to do if you are writing a historical as you do have to be conscience of the historical mindset.
Anyway I am not entirely sure which is the easier task for the imagination -- to create entirely new characters ho move about the landscape of your mind, or to have inspired by real live people characters moving about that landscape. And what if the landscape is inspired by the landscape they naturally inhabit? Is there a fine line between reporter and novelist?
I s till remember a professor asking me where I had seen a specific image, and I had to admit in my mind but it was such a striking image that I thought it worthy of inclusion in my journal of images that I was keeping for the class. The professor and I did not get on...