First of all I have to say I find the way players have been treated in this forum very disrespectful... Players haven't exploited this game, they didn't hack it, they only adapted to the game you have made in order to play it the most efficiently way.
Now putting that aside, the repeatable quests are just a symptom of the problems of the game, and instead of fixing the underlining causes you insist on just nerfing the quests again and again.
The dev team should instead be asking themselves, why do the players build so many goods manufactories and not enough workshops? what can we do to lead players to correct this imbalance so that players don't have to rely so much on these quests?
Now there might be other reasons, but I can see mainly two reasons this happens:
First one is an easy fix. Several players build their city to be the top ranked players, and since building loads of goods manufactories is the best way to to gain points, that's what they do. Now this is a really easy thing to fix, just decrease the amount of points that the manufactories give and increase the amount of points given by workshops. There you go, players that want to attain the highest score will adapt and build more workshops and less manufactories and they will have more supplies and less need for the quests.
If this was the only issue, it would be really easy to solve. Unfortunately, its not the only one, and its not even the main one. Players build so many manufactories because the amount of goods required to play the game is ridiculous. Why? Because the battle system is so poor that players find themselves obligated to negotiate to be able to gain any provinces after a certain point. For me this is the crux of the problem.
Now i can almost see you thinking, but we have to limit the provinces that you can win, otherwise players would end up with too many expansions and high boosts and we can't have that. I accept that, but then, I rather you put a limit to the provinces you can scout and say: for this time in the game this is as far as you are allowed in the game.
At the same time, make it that within the limit you have set, the fights are winnable by anyone willing to fight. They don't have to be easy, but they shouldn't be impossible. Make it so you only win them if you fight manually for example, or give massive losses to players who auto fight, so that each provinces still presents a challenge to conquer, but make it possible to get them without having to resort to negotiating.
As more content is release, expand the number of provinces you can do, giving players a chance to win more provinces.
Yes, some players would still complain that they would be blocked in the map after they had conquered everything that was available to them, but it would be a more honest way to stop players from amassing too many expansions and high boosts than what you have now.
This would also mean that players wouldn't need to negotiate everything, reducing the amount of goods needed for the game, which, combined with the points change, would lead to players not having so many goods manufacturies and having more workshops. Which in turn would create more balanced cities and less need for players to do quests over and over just to gain supplies.
It would also mean players would have a bigger incentive to learn how to fight, and explore the game more fully and be less bored as they would have something else to do besides collecting stuff. Oh, and those military Ancient Wonders would actually be of use, instead of being something for us to laugh at.
Some players would not fight because they don't enjoy it, they would still be able to negotiate, but I believe that most players would love to be able to fight again and have more balanced cities.
Fix the points system, fix the battle system and the quests won't be an issue anymore. Stop attacking players for making the best they can do with the unbalanced game you have designed, and fix the underlining issues.