I don't know if this has already been mentioned, but maybe in every ocean there could be an island with nothing but a coloseum on it, and every 3 days or so, there will be a tournament.
If you beat an enemy in a battle, there could be slaves that are brought back randomly besides the resources. Besides other things, you can train it as a gladiator, and then can arm it, train it, and then enter it in a tournament.
In a tournament, there are some qualifying rounds, that eliminates all the lowest gladiators so that it is even enough for a bracket. Then, you pit your gladiator against an enemy. if you gladiator wins the first round, you get 1 culture point. If he wins the second, he gets 500 of each resource. If he wins the 3rd, then he gets 3000 of each resource. If he wins the 4th, then you will get 500 gold. If you win the finals, you get 10000 of each resource, another 500 gold, and 3 culture points.
Rounds will be held every 3 hours. And in between that time, you can change your gladiator's weapon, or armor to get the best over the enemy. You can also use potions that help him out.
Just an idea, but I know it will never get passed because it is too complicated...