I've tinkered with the idea that biggest missed opportunity is giving each district dual purpose. - Campus - Wide vs Tall, where it rewards yields based on if the city is going ot be high pop or low pop. - Theatre Square - Culture vs Tourism, where it generates more Great Works, or boosts the Tourism output. - Commercial Hub - Gold vs Trade, where Gold helps generating more Gold, while Trade increases the Trading opportunities. Each district would have two sets of buildings tht you can mix and match to suit your needs.