One note to make is that the IZ, uniquely of the other yield districts, has and adjacency card but does not have a building card, nor has it ever. Obviously, originally being able to stack regional buildings would have made this blatantly OP, though even today +100% from buildings would mean +9 production, which isn't awful. For reference, Theatre squares' buildings give 8 (2+2?+4), Campus' give +11 (2+4+5), and a C Hub's give +15.
Gold is clearly worth less than other resources, hence the CH buildings give more, but now that I look at it, I'm really surprised campus buildings give so much science.
Anyways, to chime in to the prior discussion, I am glad people have identified that workshops in particular exchange so much production now for production later. Yes, unlike gold, you can't actually save production from turn to turn. (Although I rarely find myself with nothing to do in the mid game.) Perhaps the project Industrial Zone Logistics, instead of giving gold upon completion, should have some kind of production boost (like n% of the project cost) available to the next building/district/wonder you produce there- then you would truly have a "logistics" project preparing to make something, and you could run it in anticipation of unlocking things or just as a way to farm up some GE points and not be too "wasteful" of your production. Either way, the release model of "production costs based on tier in the tech tree" could really use a pass to "prod costs based on what it does." Units have the same issue. This is why the workshop is so pricey.
I mentioned it in a different thread, but the mechanics of factories and power plants are such that they actually have both local and regional yield values currently coded in- the displayed number in the city report is just the highest applicable one. They are set to be the same, but you can see the difference when you have James Watt. He only boosts the local yield. Nikola Tesla boosts both. This is very sad if you were hoping to exploit the Mausoleum and Magnus to get a bunch of +7 factories stacking on one city, or if you thought you could project a +11 factory aura.
In lieu of universal stacking, I would propose the following change:
Instead of cities gaining
factory yield = max(local yield, [regional yield 1, regional yield 2,...])
they instead gain
factory yield = local yield + max(regional yield 1, regional yield 2,...)
IE, you always get the strongest aura in addition to the extra +3 if you actually have a factory in the city.
This way, factories and power plants will always benefit a city that has them, but can still benefit from having coverage. At least that way there's a reason to build IZs in more cities, even if it isn't quite 'optimal.' You'll never put inexperienced players into the noob trap of building lots of factories and power plants, and ending up costing them 5 maintenance for the luxury of 2 GE points. I abhor noob traps in any game - especially when the factory's tooltip will proudly declare +3 production when it in fact might give 0. Building a factory/pp in a city that already has coverage should do something to boost your production. The game just doesn't feel like you're properly industrialising with the current rules.