Despite the conspiracy theories, what would anyone have to gain from assassinating her?! She is a bigger headache dead than she ever would have been alive. She was divorced, no longer a member of the Royal family and could frankly, do what she wanted. Sarah Ferguson has had some strange liaisons since her divorce, but no one has sought to bump her off. And given that Charles has been banging on about being Head of Faiths, the fact that Diana was (allegedly) about to marry a muslim (which I don't believe for one minute - they had only been "seeing" each other for a matter of weeks) should have had no impact whatsoever. Plus as has already been pointed out, a car "accident" is hardly a sure fire way of assassinating someone.
3 x the legal limit, plus high speed chase for which Paul was not properly trained, plus no seat belts was always going to end in disaster - just as it does (very sadly) every single day on our roads.
I feel sorry for her sons. It can't be nice having their mother's life and death raked over in the media every single day.