I don't think agendas changing every era is a good idea at all. It would make leaders seem comically unstable. Also if I decide I want to please this person or that, and steer my strategy toward it I'm doing so under the guarantee that it will yield positive results. Having them flip over on me would be infuriating. It would just encourage a complete lack of involvement, because being involved would never be worth it.
Moderation is key: If all techs and civics available to research are of roughly equal value they will highly approve. If there is great disparity (techs have been left behind) they will disapprove.
Hero of the Underdog: Very high opinion of civs with low scores, slight malus to the civ with the highest score.
Contrarian: Loves civs everyone else hates.
Globalist: Maintains and likes civs who maintain mostly external trade routes.
Isolationist: Maintains and likes civs who maintain mostly internal trade routes.
Addictive personality: This leader has found what he/she wants out of life, and they want more; all of it, in fact. This civ will try to horde a random specific luxury. They will like civs who provide it to them, and absolutely detest anyone who withholds any. They will stop at nothing to acquire all of it.
Love at First Sight: Something just clicks for this leader upon meeting that special someone. This leader will be unnaturally attracted to a random civ and will always have a high opinion of them no matter what happens.