Maybe it's just my Civ experience talking, but I keep thinking that the Produce X tasks you can give to cities should scale off of, you know, Production. As it is they are just a multiplier to however much they are producing. Thus production heavy cities get left kind of in the dust if they're in one of the idle modes, while gildar/research/mana focused ones just get better at what they already do. If making all of them scale off of production is unacceptable, how about just the Produce Wealth task, using that production for economic gain? Or perhaps a new task that lets you convert resources, like excess metal (I have so much of this crap) being turned into profit at a rate based off of production.