Definitely a sensible thought there. I'm not so familiar with all the games on Nutaku (came here with the launch of the uncensored version of Crush Crush), but I've been playing a game on Steam and Kongregate called Crusaders of the Lost Idols and this is what they do there. It has events featuring two characters and three challenges based on the event's theme. In October 2016 they got back around to where the events had first started and so they started repeating events. All the same characters and challenges from the previous year are still there, but they add a second tier which introduces two more characters and three more challenges. It definitely keeps things fresh for the players who were around for the previous version of the event.