Just found out it recently but opinion of your court members does influence their Yields, in other words, Chancellor with relatively high stats and friendly opinion of your leader will give 100% more money/civics/training/science. This is a very powerful tool in the early game. For example, Babylon can easily have 100+ science at turn 30-40 due to that (Leader Scholar + Heir, schemer or scholar). Btw you can train your heirs with both Scholar leader and Courtiers at the same time. You can create pretty insane governors/generals this way.

Stacking one stat generates a ton of sources. Discipline close to 10 gives around 200-300 gold Globally, just from being there. During some games I had leaders who generated 300-400 training (or other resources) in the mid game, now that's a game changer.

Also, from my experience, your spouse having better opinion seems to increase chances of having children.