Honestly if you quit the game over the addition of a 2 value information display, I'm not sure how much longer you would have stayed.

I really don't see it "dumbing down" the game. It's a convenient information display that shows specific information about a monster.

Actually I think a decent compromise would be this:

Aggro display: Data is acquired after encountering this monster and triggering the response, or not, at least once.

Level display: Data is acquired after fighting the monster (pass or fail) at least once.

Still have the option to toggle it on or off. That way you'll only have the info for monsters you've encountered/fought before. Maybe take it a step further and say the data is only acquired after defeating the monster once.

Also there is still a bit of mystery left in the game with the aggro indicators. Take Efts for instance, they operate on sound aggro because if you turn off run you can walk right by them without any problems (outside of a small range). Also within a certain range any action that makes a sound will make them "look" at you (such as pulling your weapon out). The sense of tension and suspense can still exist if you know the specific ways to get around a monster.