I think that "Adventuring" has always paid well in all fantasy games. There simply is no better way to make huge amounts of cash than find monsters lairs and take their cash. I find this in all forms of fantasy game play. I remember in a pen and paper game of rolemaster many many years ago I once handed a bunch of NPC elvish refugees enough gold to build a new town. Elemental seems a lot like that. The wealth of an ancient civilization was scattered all over the world - humanity was almost wiped out in the war with the Titans, the only thing out there in the wilds are the monsters and it's a well known fact that monsters LOVE the SHINNY stuff.
So the wealth of the world has been redistributed to the Monsters - you want it back - go get it back.
I understand that you want to play the game as a civilization builder not an adventuring game. I don't understand how the monsters having gold hurts you? you make it sound like you have a plan for civilization all worked out (and you're doing well with 10 cities by the way) and having your army kill a bunch of marauding trolls and redistribute some wealth into your civilization is a bad thing? Like the accountants have gone on strike? 
I agree that it may not be "balanced" - I agree that cities should create a little more wealth - Tax settings would be good. But I think that "balancing" a game so that no matter how you play it you get the same rewards doesn't work. I love outfitting a bunch of adventurers - with one of my kids in the lead, and having them go questing to support the kingdom and see what they can uncover. Personally - I feel that it makes sense to do that as it is part of the game and the fact that the wealth is out there in the hands of monsters makes perfect sense in that game setting.
I personally have a lot more trouble with FOOD. Bring back the sovereign ability to fertilize land that they had in the beta. It cost essence. so you wouldn't want to do it too often but the odd extra fertile land tile at the cost of some essence would bring a balance to the game that isn't there at the moment.