That would be interesting.

However, I am quickly learning (and the more veteran players will tell you) that watching your neighbors/adversaries is a huge part of the game. You are right, the buildings you make broadcasts to the rest of the players what you are doing/mobilizing (except secret weapon bases and bunkers, the are invisible:). Good players will study the newspaper reports, note buildings and building levels, and keep an eye on who expands where.

I think what you're suggesting would change the way the games play out. Would introduce an element of luck to the game. It is an interesting idea, dont think that I am bashing you or anything, but maybe could be a good idea for a special game mode? Invisible buildings unless within sightrange or revealed by agents.

2 things need to be consider

1) How much player need to invest into gaining important information (in another word, How easy to information)
and is that the direction the game designer want to go ?

2) Is it in the budget or possible to gain profit from investing into making the change.
I think this part is the most reason why this game lack of feature.
(You can see a lot of my suggestion tend to using old system in place to build a new one)

Personally I want to see the "shadow" feature like unit in COW. display the last know information and predicament.
still wait for News rework and Spy rework LOL

We could effectively hide them - but decided against this option. Basically nations do know about the general buildup of forces by other nations. It's not a secret at all - consider factories, camps, barracks, staging grounds, transports, warehousing and all of the other million parts of modern infrastructure needed.
So if a nation starts expending north of 10% of it's GDP on military - that's information available on the internet today. (Saudi - I am looking at you). Do we know where their weapons are coming from and where they are being stored, maintained and trained (troops) - yes pretty much in detail.