A very good observation about levels of abstraction, Jiminov. But I disagree with your conclusion.
I don't think the entire game needs to have the same level of abstraction. In fact, I think the opposite.
Sorry for being pedantic about this. I think "level of abstraction" refers to how general or specific a game feature and subsequent player actions are. Every game has essential features and other features. Differing levels of abstraction for these features are necessary to put emphasis on the bits of the game the designers want the player involved in (lower levels of abstraction) versus features the designers want in the game, but don't want the player too involved in (higher levels of abstraction).
My quick assessment (arbitrary scale) puts the levels of abstraction in EU I as follows:
* Technology - very high. The player can only manipulate how much money is invested.
* Trade - high. The player can send traders to different CoT's, but getting into the CoT and getting money is outside of the player's control.
* Colonization - medium to high. The player sends colonists. The player has more control compared to Trade (a chance of success is given to the player).
* Military - medium. The player builds different types of units, moves the units, and chooses how much maintenance to pay on them. On the other hand, the player has no control over combat.
* Religion - very high. the player sets tolerance to the different religions. Consequences (revolts, diplo relations) are outside of the players control.
* Diplomacy - low to medium. The player can take many different actions that directly effect relations.
* Other economic - medium to high. The player can build manufactories and so on. These have specific economic effects that are of a "low" level so are worth calling out.
My conclusion is that EU I is a diplomatic/colonization/military campaign game, with some other bits thrown in to make it work. It is not an economic game, even though economics have a profound effect on the game. The measure is what player actions can effect things. The player can only effect economics indirectly. And to your argument, technology even more indirectly.
Now, this is 15 minutes of analysis, not the several days that the subject needs, so there is probably some real crap in this post, but...
And to your specific point, I like a high level of abstraction for infrastructure.

I'm interested in diplomacy, wars, and so on; not the internal transport network, or whether I can spin thread in a cheaper manner, and so on.