Concerning Improvements being Bombarded away, I like Great Wonders placing Improvements because those Improvements cannot be Bombarded away.
Of course the City that builds the Great Wonder must be strong or guarded to prevent it from being captured or the Improvements are lost.
Concerning the AI building Wonders and Improvements, it is best to set the AI to Build Wonders or Improvements from the start of a Game because when at War and the Cities are being attacked, the AI will tend to build Units rather than Wonders or Improvements. IF the AI has a city that is not being attacked, that city can build Wonders and Improvements later in a game. IF the AI is building a Wonder or Improvement, you can Bombard and attack that city with strong units and that generally will cause the AI to stop building the Wonder or Improvement and build a Unit.
Events where you want an Improvement to start Auto-producing Units later in a game can be handled by having the AI build a Great Wonder that places the Improvements in the Cities. Set those Improvements to require a Resource that will be gained later in the game when you want the Improvements to start the Unit production. The Improvements are there but cannot Auto-produce until the Required Resource is obtained. This provides more control of the Improvements and the AI will build the Great Wonders in the beginning of a Game. If you set an Improvement to build a Unit every 10 turns for example and the Improvement has been placed in the Cities for at least 10 turns before the Required Resource is obtained, the turn that the Required Resource is obtained, the Unit will be produced. So do the math to get what you want.
In order for a Great Wonder to place Improvements in Cities, it Must be Built in the game. If you pre-place a Great Wonder with settings to place Improvements, it will not work.
One work around is to have the Great Wonder immediately start producing a Unit at a slower rate or even a different Unit as well as placing Improvements that will start Auto-producing the same or different Units later with a Required Resource. You can then control the rate of production and or Unit type and when it will happen in a game. Because Great Wonders can place Improvements in ALL Cities on the same continent and in All Cities, this allows you to have the Great Wonder place two different Improvements that can then start auto-producing Units at different times in the game simply by setting different Required Resources for the Improvements.
You have to think of this as the Improvements are there in the Cities but because they do not have the Required Resource to be built, they cannot function to produce Units. Later when the Required Resource is obtained, the Improvements can also be directly built and the pre-placed Improvements will start the Unit production. I will add that although the Improvements cannot start Unit production until the Required resources are obtained, the other settings for those Improvements work from when they are placed.
You can pre-place an Improvement yourself with a Required Resource that will be obtained later to do the same thing a above but unlike being placed by a Great Wonder, the Improvements can be Bombarded away.
This is all AI manipulation to get what is wanted in a game... lets call it "Fun with the AI"
