You can earn certain rewards again, including Boosts for the Host Island, Monsters and Costumes by replaying an Act in the Clubbox!

If you have already unlocked the Clubbox-specific rewards for a given Act (such as Stage Props and Performers), they will be replaced with alternate rewards, such as Diamonds or Sticker Packs. 

Replaying Acts is a great way to earn additional rewards while continuing to earn valuable boosts for your Islands!