First, let me outline how I understand the process of adding new city improvements:

In order to add new City Improvements (ala Hut, Inn, etc.) I need to:

1.) Create the tile (or tiles, if I want to have a nice building-in-progress tile as well)

2.) Copy the newly created .xml files from /documents/my games/elemental/tiles into /program files(x86)/stardock games(x86)/elemental/data/english/core tiles/improvements

3.) Edit one of a variety of .xml files (such as KingdomUnlimitedImprovements.xml or KingdomSpecialImprovements.xml) in the /program files(x86)/stardock games/elemental/data/english/core improvements folder to let the game know:

1. to make my newly created improvement available
2. how much it costs to create
3. what it does

So, my question is: Is the above correct and ideal?

If so, adding a variety of new buildings by different modders would quickly become difficult, as each building would have to be added into the same .xml file (e.g. KingdomUnlimitedImprovements.xml) and updating the game would most likely overwrite these.

As for the suggestion:

I'm probably missing something, but if not: instead of having a single  .xml file containing the detail information for each improvement, how about using a folder containing single .xml files for each improvement (one .xml per improvement)

To explain this further:

Just as you have (for example) a F_Barracks_01.xml in /Core Tiles/Improvements which contains the graphical information needed to assemble a Fallen Barracks, we could have a /Core Improvements/EmpireSpecialImprovements folder into which we could drop a F_Barracks.xml that would contain all the information the game needs to actually make sense of the building (what is it, what does it cost, what does it do, etc.)

This way no mod would interfere with any other mod or with official content.