It's rather hard for me to have any opinion about Camilla since I don't remember her ever saying anything about anything, and I don't even know what she thinks about her charities or royal work, or even what her focus might be, if anything? Why doesn't she ever open her mouth and say something?
You can read her speeches at the Prince of Wales' website. I think she cares deeply for the topics she talks about in public.
part of a private conversation between Charles and Camilla is enough to form my opinion of them and of their relationship (from the infamous Camillagate-tapes):
Camilla: I do love you and I'm so proud of you.
Charles: Oh, I'm so proud of you
Camilla: Don't be so silly, I've never achieved anything.
Charles: Yes you have.
Camilla: No I haven't.
Charles: Your great achievement is to love me.
Camilla: Oh, darling. Easier than falling off a chair.
Charles: You suffer all these indignities and tortures and calumnies
Camiila: Oh, darling, don't be so silly. I'd suffer anything for you. That's love. It's the strength of love. (End of quote)
Ever since the "non-achiever" Camilla accepted her darling as husband, she set out to achieve something because she realised that from then on, loving him was not longer enough to make him proud - she became a working princess in her own right. And she does a good job at it, the people she meets tend to praise her afterwards for her compassion and interest.
Plus whenever we are allowed another glimpse into her private life via the media, it turns out that she helped others in secret, without wanting or searching for the spotlight.
I like that lady, really I do!
Plus: if you can accept that these two were not telling each other some sweet lover's lies 18 (!) years ago but meant it, then maybe it's understandible that I believe not vindictive Diana was the victim but dignified and loving Camilla who never wanted something out of her relationship with Charles but the chance to spent a night alone with him and who did not dare thinking of a "happy" christmas because it hurt her too much (from the Camillagate-Tapes
Camilla: It would be so wonderful to have just one night to set us on our way, wouldn't it?
Charles: Wouldn't it? To wish you a happy Christmas.
Camilla: (indistinct) happy. Oh, don't let's think about Christmas. I can't bear it. (End of quote)
So I hope these two enjoy their christmases together these days...
To come back to Diana: around the same time, at christmas 1989, Diana phone her lover James Gilbey and told negative things about Fergie, was interested in her pictures in magazines, asked herself if she was beautiful enough etc.