I would like to see another level(s) added to them. But… I do not think there would be an ROI for the development time. Would enough users spend diamonds over the settlement lifetime to make up for the development costs? And part of the development cost would be allowing users to do the entire settlement again and earn a second level 1. Not everyone wanted to store them away when having something more valuable to put in that space, so they would have just deleted them. But.. How could they have just deleted them??? Hey we have folks here advising someone to sell a higher level CC to make room for something more valuable.
Before the latest Power LEAP in event buildings, the settlement buildings were well worth the time to complete AND try for the secondary rewards also. I am sure they more than earned their ROI from the initial development.
For Japan the Yggdrasil was way OP! And the Greater Runestone with 2 attack, 2 FP, 1 good and some coins in 4 tiles! An SoK gave ONE FP in 4 tiles and players had rows of them, the Runestone was twice that! When it was introduced, it was a massive per tile income for a building! Players had fleets of ‘The Ship’ with 8 attack, 4 FP and 15 goods in 21 tiles.
Same with Jade statue: 3 FP, 5 Goods and 10 Guild goods in 4 tiles!! That is 3X the production of an SoK PLUS goods and guild goods!! And it was nothing to just keep looping the Eqypt settlement and grab Ancient Obelisks. Yeah, they were no SO but with 6 Defense, 2 FP, 4 goods and coins, that was an excellent use of 4 tiles!! And Egypt did not need to be babysat or dickered with all the time. Just pop in every 8 hours or a couple times a day to battle and start productions. Eazy Peazy to complete in time. Not like Vikings where you had to be dealing with it all the time to get done in time.
Mughal Empire.. I went through it once. It is the most unfriendly, tedious and frustrating settlement to complete. Your mileage may vary, but I did one and never started another one. By comparison, I had 7, 8 or more of the Ancient Obelisks in a city before Flying Island was even a thing. And no, I have never built FI