On the subject of Sarah's charity work, I'd like to quote a little from the book "Fergie Confidential" by Chris Hutchins (1995). This is by no means an officially sanctioned or cheerleading biography. I'd say it was a balanced and fair minded look at Sarah's life up to then, the positives and the negatives.
Quote: "Her apparent unselfishness won over many people who came into contact with her through her charity work. [...] 'She puts in so much of her own free time for us', said Peter Cardy, director of the Motor Neurone Disease Foundation. 'Sending us hand-written notes when she is supposed to be on holiday, dashing off to gory medical briefings when she is supposed to be off duty [...] That tells you about her commitment'. [...] Away from the spotlight, the Duchess made several private visits that were not listed on the Court Circular to the Trinity Hospice. [...] The hospice was not one of her 'official' charities, butsbe helped its fund raising activities and made surprise visits to cheer up the patients".
A patient then goes on to say that "she takes a real interest. It is not just a case of doing her duty".
Now, admittedly, this quote is from more than 20 years ago, but I can't believe her attitude to charity work would have changed so drastically. It's hardly consistent with the image of someone who engages in charity just for the publicity and the travel expenses.
As for the question of how effective her support is nowadays - I believe the tickets for the Not For Sale event she spoke at in California were being sold for several thousand dollars. There are still many wealthy Americans who will pay significant sums to charity to be able to rub shoulders with Sarah.
No doubt she is getting some first class flights on expenses, and I'm sure she combines some charity trips with leisure and business, but I don't have a problem with that. The work she is doing is benefitting real people. As people have suggested, I think she does have a certain need for public recognition, but I think she wants that recognition for doing something that really matters, something that genuinely helps people. She has gone through so many tough times in her own life, and I think that gives her a real sense of empathy for the suffering of others.