I found the following on another forum site, might not be a bad idea for CIV V or expansion or PATCH even?? 
[I've often thought they should upgrade the graphics of the military unit as the ages change, but, they maintain their present combat values from when they were created and their CIV IV experience bonuses. There would be era "triggers" like when someone hit's tanks or battleships etc. the game would automatically upgrade the graphic icons of all the other nations, so things like knights, spearmen, swordsmen, axemen, archers would upgrade in "graphic" to something proper for the era change.
This would then give the proper look of an infantry/cavalry defeating a tank or helicopter, even though it has the combat values of a spearman or whatever ancient model it used to be. It's the psycological aspect that a spearman shouldn't be able to defeat a tank, helicopter, whatever of modern times, but, it's really not the picture that is involved in the combat calculation it's the units combat values. Seems like it would be a simple task. Dunno, but, seems that would quell those that just can't stand that a spearman defeated a modern tank or battleship etc.
They could still then upgrade the "combat values" of the units as the game allows this, and the icon graphic would still look correct for the era.
Also something this would do would be to add even "more" to the fog of war, is that musket unit really a full fledged musket unit or is it merely a militia unit?
Think about it this way, when you see a charge of men or cavalry coming at you can you really tell which ones are "green" and which ones are "veterans"?? ]

[I've often thought they should upgrade the graphics of the military unit as the ages change, but, they maintain their present combat values from when they were created and their CIV IV experience bonuses. There would be era "triggers" like when someone hit's tanks or battleships etc. the game would automatically upgrade the graphic icons of all the other nations, so things like knights, spearmen, swordsmen, axemen, archers would upgrade in "graphic" to something proper for the era change.
This would then give the proper look of an infantry/cavalry defeating a tank or helicopter, even though it has the combat values of a spearman or whatever ancient model it used to be. It's the psycological aspect that a spearman shouldn't be able to defeat a tank, helicopter, whatever of modern times, but, it's really not the picture that is involved in the combat calculation it's the units combat values. Seems like it would be a simple task. Dunno, but, seems that would quell those that just can't stand that a spearman defeated a modern tank or battleship etc.

They could still then upgrade the "combat values" of the units as the game allows this, and the icon graphic would still look correct for the era.
Also something this would do would be to add even "more" to the fog of war, is that musket unit really a full fledged musket unit or is it merely a militia unit?
Think about it this way, when you see a charge of men or cavalry coming at you can you really tell which ones are "green" and which ones are "veterans"?? ]