Yes, people mostly seem to remember the "big scandals". Maybe because that are the things the media mostly reported about.
I think there were two things the media mostly reported about with Diana, and sorry to say, they weren't her work with AIDS or landmines (although I'm sure those will be remembered by those who follow royalty). I think that before her death, Diana was mainly known for being beautiful, compassionate, and a fashion icon. She became this image of the "perfect princess" and the thousands and thousands of pictures taken of her in the 1980s and early 1990s aren't going to disappear. When William marries, or when he is crowned, or when Charles becomes king, the footage of Charles and Diana's wedding is going to resurface, and the media will show the pictures of Diana holding children, and even people who don't know much about Diana will be captivated and think "Oh, she was a fairytale princess." I know, it's inner beauty that counts, but in reality everyone judges people according to their outward appearance and the truth is, whatever she did in her life, Diana was very photogenic and she had a very sweet way with people. Future generations who look at pictures of Diana are going to notice these things, just like many people did in the 80s when they saw images of her for the first time.
The other aspect of Diana's life that I think was mainly covered in the media was her attention-seeking and deceptive behaviour. That endless inquest pretty much dragged every fact and rumour and innuendo about Diana's life into the open, and a lot of it was ugly--her affair with Hewitt, the phone calls to Oliver Hoare, the glitzy lifestyle with Dodi that ended in a high-speed paparazzi chase.
So I think public opinion on Diana is going to be divided. People probably won't know much about Diana in a few decades' time, but by the people who know anything about her, she's either going to be remembered as the fairytale princess who was a victim of a heartless royal family, or the villain who went out of her way to destroy the monarchy.
One thing I don't see happening is Camilla becoming better known/remembered than Diana, as I think was mentioned here a while back. She rarely seems to get much media attention, and she's actually a little older than Charles and doesn't seem to come from as long-lived a family, so probably if she does become queen she will just be an elderly queen with him for 10 years or so and be forgotten a few years after her death. There's nothing necessarily wrong with that, but I think Diana is going to have a much more significant public legacy than most other people in the royal family for years to come (both positive
and negative).