One thing I do like about Zones is that it can make it a bit easier to math things out in your head. For example, if I'm a Xenophobe or Authoritarian Spiritualist empire and I have a planet that has buffs to Mining and Sociology, then I can decide to get my amenities by building an Archive District and placing a Biology Lab there in order to get a mix of Priests for amenities and Scientists to take advantage of the biology bonus, which also provides some Specialists to balance out the slaves. Once I've made that decision, I can scale things up appropriately by clicking a button. Similarly, it does provide a certain level of intuitiveness in regards to unity and science- you can get a good feel for what you need by just levelling your capital's City District and slightly adjusting it with a building.
I do feel, however, that Zones would benefit a lot from having more types of synergies, for 'support' zones as opposed to 'main' zones.
There's a few already if you look for them, such as a planet with a bias towards Minerals being a good place to put a Unity world, since Rare Crystals -> Unity, or Urban zones being a good partner to produce amenities for Rural-focused worlds since they also let you move resource buff buildings into urban slots. More ways to intertwine zones like that would be an excellent step forwards, I feel. Options such as Priests and Rural Strategic Resource Extraction buildings, that add a resource to Zone jobs that other Zones on the planet can use, are where I've been getting the best gamefeel out of using Zones.
Basic resources have relatively few options, so I think there's particular potential for having more buildings along the lines of the Bioreactor and the resource gatherers added to them- possibly even entirely new zones. For example, being able to partially convert a basic resource zone into a maintenance zone- say, a 'Food Processing' zone rather than a 'Farming' zone in order to convert your farmer jobs to a 'factory worker/food processing' job that partially replaces food production with amenities and/or consumer goods- would be a fantastic reason to desire a fertile garden world to rear a decadent trade economy on. Or a 'food packaging' zone that gives food and trade value. Similarly, you might be able to get a 'Hard Labour' zone for mines with the right civics or ethics, so that you can beat crime by building mining zones to throw your dissidents into.
(Not that there isn't opportunity for specialist zones to do this too- Priests turning sources of unity into sources of amenities, or Masterful Crafters turning consumer goods into trade for imports, are both good examples of what could be done. I could see civics like Masterful Crafters or Anglers being made to have upgraded or option-combining versions of pre-existing options to generalise your zones, for example.)
You can do this with buildings, but only to a degree, since buildings are non-scaling and many middle-stage goods like consumer goods are hard to build without a dedicated zone anyway. And the fact that these synergies mostly exist through buildings then limits your options with buildings- my experience so far is that a well-developed planet will have a capital building, a police building, two or so amenity buildings, and a bunch of buildings that are only able to expand on what your zones do anyway, meaning that there's only one or two building slots left free for your personal touch. Moving some of that choice into the zones themselves would thus in turn make it more fun to use buildings, since you can now decide between how much you want to rely on zones versus buildings versus imports to maintain your planet.
In summary, I like the ability to decide on what I want and then get a reasonable balance of stuff by clicking the upgrade button, but there's not enough single-planet synergies for the two City District options to be satisfying on their own. Targeting Basic Resource zones, as the area with the fewest choices to make on any individual planet, would seem like the lowest-hanging fruit to increase the number of single-planet synergies you can make with zones.