I've been through several replays of Hard NewGame+ and my kingdoms always tend towards looking identical, or near enough as to make no difference. And that is because you can devise an optimal build for the game, including any self-goals, like autarky.

What would help is a much larger tech tree but that you do not get every tech. For example, you might only find blueprints for 3 of the 8 lift techs, so that playthrough's kingdom would necessarily look different than the one that got different lift techs.

I have no idea what to do about the production model. Adobe and glass are no more difficult than simply not gathering raw materials, and timber can be balanced with coal and powered lift/propulsion, but cotton and iron ore eventually either need to be dumped or warehouses built. So far, the best answer I've come up with is start a new game...

What about maintenance/repair?

If houses needed adobe from time to time, it would be a reason to keep that industry going. If fins needed spare parts (iron) or balloons needed canopy repair, again, a reason to keep those things going. Don't make it a pain -- just if the worker or resident notices something that needs fixing (just a percentage chance), subtract the goods and carry on. Or add a building that hires handymen, who go around fixing stuff.

As the stuff wears out, it becomes less and less effective, like propulsion and lift provide less and less boost until sometime they fail completely and fall off, a complete loss of the building materials. As housing degrades, it provides less and less comfort and/or health

Might not be worth bothering with in this game, as even a Hard NewGame+ only takes a few hours, but if there's a new game in the works, maybe that could integrate preventative maintenance. Because as is, once I build maybe 6-8 fins, I have no more need for iron. Might as well chuck the ore overboard and delete the forges.