I was wondering how about if FG introduces new realm concepts?
Rather than introducing new characters and always increasing levels of Towers and spells in the game, It would be very good idea to start having new realms from the start.
For example Ghost Realm, futuristic Realm etc.
Everything needs to start from scratch, however the gems, the gold and other attributes remain the same. Rather than just spending the gold on immaterialistic thingd now, you can start building the new Realm.