Maybe I missed it somewhere, but is there, or could there be, an option so that when you click on post activity and click view all posts made by you, that you can have all of the posts made by you with new replies since your last viewing of that topic moved to the top of the list? I've got 19 pages to scroll through to keep up on topic posts. I'm sure there are people with a TON more than me.
It would be helpful to have anything that's been replied to that you didn't view yet moved to the top of that list so they are all on the first page of that list. Maybe put them in date order after that?