^ excellent observation about the balance act between maintaining high approval and expanding your cities to get the most FIDSI

IIRC leveling a district gives +2 science, +2 dust, +2 influence, and +15 happiness.



Structuring your city in such a way that you can level your districts typically means that you give up roughly 1 exploitation per level (if you ignore levels you can expand your city area by 3 tiles per district, but you can't sustainably add more than 2 tiles per district unless you increase the number of non-leveled districts).



In the early game, an exploitation on "ordinary" terrain gives 3 FIDS in some combination. That's half the FIDSI you get for leveling a district, even if you ignore the happiness. If it's a trade-off between leveling a district or getting an anomaly, then I might go for the anomaly (especially if it gives a happiness bonus), but with ordinary terrain the level is usually going to be a better option.



Even if leveling a district gave you less FIDSI, happiness raises food/industry (and on an empire level, science/dust) by a percentage, so the bigger you get, the more you would tend to prefer the happiness over raw FIDSI.



However, in the late game it's possible to reach a point where you have more happiness than you know what to do with (particularly if you can sustain lots of luxury boosters). It's also possible to get buildings that will greatly increase the FIDS you get per tile--there's a building that gives you +3 industry on terrain with industry, one that gives you +3 food on terrain with food, two that give you +3 food on exploitations, etc. Under ideal circumstances, you can get over +20 FIDS per exploitation tile above the base terrain output (and much more on rivers), which starts to make the +6 FIDSI for leveling a district look paltry in comparison.



So you may eventually find that increasing your city's area becomes more important than leveling districts. In my last game, most of my cities eventually switched to a hybrid approach where they leveled enough districts to maintain "fervent" status, but also had some districts that were positioned purely for access to more terrain...and it wouldn't surprise me in the slightest if a careful analysis revealed that it would have been better to let my cities drop from "fervent" to merely "happy".

I belive only cultists can achieve a level 3 district now, and then only on their cental city tile. All other districts are capped at level 2, including all other factions central cities.

If you build your districts so that you get the most tiles available you will earn 3 tiles per new district.

If you build them in an efficient way (two adjacent lines), you will only get something like 2 tiles per district, but you will get additional bonus due to level 2 / level 3 district and extra happiness.

So yeah definitely worth it.

The problem with not leveling up districts is the happiness penalty each level 1 district incurres. Building up to level 2 basicly reduces this penalty in half. Check out my thread on expansion disapproval for more details, but this plays a big role later in the game once % modifiers become more meaningful to your FIDS output.