I honestly think each season of Cookie Clicker should be doubled in content as another heavenly upgrades.
Christmas should have Ms. Claus joining the fray with her brand of transformation and upgrades.
Valentines should add more Valentines cookies or situations.
Easter should add either St. Paddy content or new Eggs.
Halloween should add some Halloween folklore monsters like vampires and Frankenstein.
Business Day should add Business-themed cookies.