Is there something specific about the Feynman appendix that you think hasn't aged as well, or is it more that you've squeezed all of the juice out of that fruit already?
More the latter! It's still a very charismatic text that I'm fond of, and it's of course also intensely quotable. But given its brevity it can only deliver so much.
If you want a much more detailed treatment that covers both every aspect of the technical issues, as well as the corporate and government malfeasance that lead to the disaster, consider “Truth, lies, and O-Rings” by Allan McDonald, the Thiokol program manager who would not sign of off on the launch and overruled by his executives. He had good things to say about Feynman, and definitely some axe grinding for other individuals.
Is there something specific about the Feynman appendix that you think hasn't aged as well, or is it more that you've squeezed all of the juice out of that fruit already?