Derek, with respect to your reasons why you like Yield Limits:
1. I want to make a decision based on choices, not limitations. If you want me to have a choice, force me to make that choice on factors such as up-front value versus later value (production and mana are great up front, but gold takes while to accumulate). If I see a spot with 4/4/3, let met have its fullest benefits. It is no fun seeing it and expecting to have it, then learning you can't have it.
2. Spells and other effects can increase from 5/3/3 for instance and part of the value within the choice is how to develop your choice later and not just when you settle it. When I want to specialize a city in a certain way, I shouldn't have to "remember not to increase any value about X" and factor every several turns; this burdensome micromanagement is not fun. Also, mods that increase yields by changing values or through a spell become worthless unless the 9 cap is removed.
3. Controlled Pacing: As the game moves on, my ability to improve a city beyond 9 will happen. Part of the choice is that I can "go tall" by having 3-4 cities with 12 or 15 instead of 10 cities with 9. This is far more fun, gives me a new spectrum of choice (tall vs wide, rather than forcing tall) and gives more value to the conclave/city/fortress decision. This decision gains value because with a max 9, I have the same choice every time, while if I had a town with 12, I would have to think "this would be a great fortress, but... it could also be the "best" city ever."
4. Why do we want more yields? Because some maps might "require" 5 cities with 3/2/0 as being the only options with maybe a 4/1/1. Seeing the 5/3/3 tile I saw once was in the middle of 2 other spots: a 4/1/1 and a 3/3/1 or ONE 5/3/3. This presented me a perplexing decision that, instead of making me choose between 2 bad things, or 2 good things, would have made me choose how to play that current game. Tall or Wide.
That said, the player who knows how to change numbers in XML does so because they want a different experience; making this feature in the XML puts your idea onto the field but lets the player change it if they want to.
To answer your question about motive: I want to play a "Tall Empire" with a diplomatically peaceful game with other empires, fighting through the wildlands and doing quests until I feel my Tall Empire is ready to "Pull a Ghandi".
Still getting used to LH, great work.