Rivals has three expansion decks as does Age of Darkness. Thematically, these six cover most of Catan Card Game and its seven expansions. The biggest thematic delta is Catan Card Game's Wizard & Dragons expansion; I always thought this was the weakest expansion (wrt gameplay; I *really* wanted it to work!) of the original set.
You should consider Rivals + Age of Darkess as a reimplementation of Catan Card Game + Catan Card Game Expansion Set. They are not intended to be compatible and it would be redundant to have both. (That said, I'm keeping my Catan Card Game set because it has a lot of memories being my most-played Euro, but I bought Rivals to play with my daughter as it was thematically compatible with the Candamir board game which we enjoy.)
I really want to get Candamir and Elasund. I have the 4th edition of the Catan board game and the 3 expansions but the adventures games I feel are needed to complete the set. Also thinking of getting Entdecker and Domaine since they are Catan related. I really enjoy playing Catan with my family and it is a great family series.