Orion,
Been playing your mod a few times now and, yes, I have noticed the perfomance hit. Normally, I would have subscribed it to playing a large map and too many units. I was not aware of the mine checks. It does make sense as time goes on as more roads and railroads are built, the number of units moving and tiles checked goes up exponentially!! I hope you can migrate this and will keep watch.
One other thing I've noticed deals with the resources. I know early on, you can plant corn, wheat, and rice. As I understand it, if the tile you are planting on has another resource allocated to it (which you cannot see like oil, aluminum, etc), the resource is overwritten in favor of the corn, rice, or wheat. As a result, I dont do any planting until I get into the later stages of the game when I can see most of the world resources.
However, one thing I have noticed in the later stages of game and is a complete lack of the later resources; aluminum, uranium, oil (especially), and titanium (have yet to see a game with it). I am wondering if all the AI planting is eliminating many of these "important" resources.
I am not sure how you can work around this or even allow a player to have a warning message when he is about to overwrite a resource that they cannot see yet. I would love to use the planting feature right off the bat when I get it, but I fear destroying a more precious resource. It would to help to know something is there and allow us to use the planting feature.
Just my 2 cents worth! Keep up the good work!