I agree with Thunderfall that spies should be in the casualty stats. I use them a lot, and have no real way of tracking them as they are used in the line of duty... but I do use a lot of them. If tracked, I think spies would lead my casualty list almost every game... that is because I consider it a casualty when they are "captured" for any reason. Same thing for diplomats. To me, it is a unit expended that I can't use again, and if I produced it and it does not survive the game, a stat somewhere should reflect it.
I'd also like to see cumulative stats on total shields, trade, gold, science, and food produced. Further, I'd like to see a city summary of the same info, and an automatic result ranking of all cities based on their economic output in each category. It would be only a slight additional programming effor for each city to track the use of its units (eg, amout of damage done by that cities' units, or economic benefit of engineers/frieght).
Computers are ideal for tracking such things, and it is a waste for the program not to track and report it all for us empire-builders!