Decision-making with perfect information is trivial compared to decision-making under uncertainty. The latter is a heck of a lot more entertaining for many people than the former. Not only is the ledger very powerful, so is much of the info that is freely gathered on most screens.
Why should you have an exact census of opposing militaries? Why indeed should you have an exact census of every attribute of foreign provinces? Why should their tech levels be freely known? Or their missions? Can you know all these things? Sure you can. Should it be 100% free? No, it shouldn't. Almost every decision in this game is about weighing costs. Information may be among the most important resources players have and it's 100% free.
To be fair, you probably shouldn't know all of these things, but it's not like if all this information was hidden it would suddenly enrich the game. A lot of this information can be deduced, and the only hard ones would be military forces (this involves lots of math in order to determine things like force limits) and attributes of foreign provinces (I assume this is in regard to revolt risk and the like, which would require a lot of values that wouldn't be seen outside of the provincial revolt risk tooltip, like tolerance of true faith).
The military forces aspect can be partially circumvented regardless just by keeping an eye on your target and waiting for them to get involved in a messy war with lots of battles. The AI is very bad at coping with attrition and manpower losses during such a war.
Of course, I assume this is why you mentioned this:
IMO, the quality and quantity information available to players about everything not in their own nation should be a function of how much interaction that player has with the rest of the world. It's not just about the Espionage idea group. It's about the entire structure of the game and it could be made much richer in this regard.
Which only introduces uncertainly in regards to major powers; minors/OPMs are pretty easy to determine forcelimits and standing armies on even without vision, and their manpower pool is irrelevant because they will be unable to rebuild a standing army worth mentioning during the war once their army gets wiped.
All you'd really be doing is adding uncertainty to the game for the sake of adding uncertainty, and it'd honestly just be kind of frustrating in the long run. I don't want to do a lot of math to determine the forcelimit range (accounting for autonomy and things like colonial nations or vassal subject forcelimit bonuses) on a major power like England, and such math is not only time consuming (for SP) but also unfeasible for MP games.
Basically, this information is 100% free because it'd be a massive pain in the ass if it wasn't, and because running all the math isn't feasible in multiplayer games.
IMO, players should have a baseline intel value that is modified by a host of factors that may be global or specific to a given target nation. The baseline itself can grow some over time with Diplo tech level, but real growth comes with investment in Diplo Idea groups
I would need to see a more fleshed out idea to form a meaningful opinion, but it doesn't sound terrible so far.