Yesterday my highest-ranked quiz was around 3800 and I had 15 in the sunglasses club, but a few minutes ago I was awarded the 'Cool Quizzes' badge for 20. So I checked my quizzes, and my best quiz jumped to around 1800 and I have 5 in the top 3000. I haven't seen anything anywhere else - did something change on the ratings?

Overnight between Sunday and Monday FT time is the weekly reranking time. It happens about 3 or 4 hours after system maintenance, and the new rankings include the ratings from the previous week being taken into account, as well as making adjustments due to the appearence in the list of ranked quizzes of newly-ranked ones. (Ratings get reported in real time, but adjustments to ranking only happens weekly.) Changes can be quite dramatic - yours was in the good direction!

The good news is that even if some of your quizzes slip back out of the Sunnies in the future (they do bob up and down a lot as they get more ratings) you keep the badge forever - congrats

Nope, rankings have not changed for a while.