True, but usually the number of troops multiply with the Industrial Revolution so Espionage should help.(a freindly trading neighbour can launch sneak-attacks just as easily).What is the purpose of the 'Steal Enemy Plans' & Show troop locations spy mission?does it have any tactical value?
I am not sure I understand the part about the number of troops. I mean I run into civs with 8 or 9 hundred units that have not gotten to the IA. It is not hard for a Sid civ to do that.
So yes you tend to see more units around as the game progress, that is not material in terms of a war breaking out. I am more interested in the free land. If there is none, then something is going to come down.
I seldom have friendly neighbors, they pretty much are unhappy with me from the day I see them. That is just the nature of high level games. If I not playing Sid, I am playing AW, so no friends for me.
I simply mark troop movement, if I can see them. If I am not at war with them and it is not a settler combo, then I have to presume war is coming.
Now if it is very early and it is just exploring or they are at war with someone else, then I am probably fine.
As has been said the Steal Plans will show all the units the civ has on the entire map for that turn. This is normally not that useful, it just cost too much.
Some exceptions are noted and the main two times I do it are,
1) late game and nukes are a concern. I want to know where the subs are or the icbm's.
2) it is late game and I just have no use for all the cash I am getting, so why not have some fun.
Down side to it is now you have to watch all of their units movement during the IBT.