There are a lot of books in this game, and it would be nice that once your character has "read" them, that the knowledge or perspective gained from such readings could have an influence on future interactions. I would just like too see that reading the books has some impact on game play, and currently they don't (except for that special necro book in the cellar). Even if it could trigger a few dialog options it would seem more immersive, and make these books worthwhile to read.

There are one or two places where this can happen, actually, but they're few and far between.

One example I can think of is that if you've read the notes in Nettie's area, and know about the poison she's using, and its treatment, you have the option of recognising it straight off, which you don't normally have (outside a check) if you've not read the book.

Reading the books does have an impact on conversations in the Arcane Tower as well.

I believe this is likely to be something they're working on.

Also there is Apothecary cellar, there you can get some usefull info from Doctor's log, that could be used in dialogue right after.

I second that. I always found it strange that you find two books about Loviatar around Abdirak and then you still have to succeed in a religion check to recognize him as a priest of Loviatar. There are more such situations.

Question is if you are even able to fail ... i mean after you read those books ofcourse.
It might be just the game mechanic, that is showing you the roll ... but you can have reduced dificiulty. O_o

Otherwise your character can be simply too slow in this particular case to connect the dots ... or on the other hand so smart so s/he is kinda overthinking. :P
Maybe the point is in recognize him as a "priest" and not only enthusiastic torturer, who was searching some inspiration in those books.

I don't know, he is very clearly praying to a 'mistress', so your intelligence will have to be 3 to not connect the dots. Abdirak was just an example, that came to mind, because you have not one, but two books about Loviatar laying around in his corner of the camp. Maybe they overlooked it.

Under the abandoned chapel you find a book containing thoughts on the value of a life. Later on the talkative skeleton asks you what the value of one life is, but the book doesn't seem at all connected with the answers that are proposed.
Maybe they are working on it.

I've developed an obsession with collecting as many books in possible in games, and I will often steal someone's book before I steal their valuables. Needless to say, I would love it if that actually impacted the game.

I think it would be a really nice role-playing touch if there were some instances where having read a book (not just people's journals that they convienently leave lying around) would actually add to your character's knowledge, and consequently impact interactions or dialogue about the topic.

Since both Gale and Astarion are apparently avid readers as well, it could even be an opportunity for unique discussion with some party members (or other NPCs).

This is true. And this is something Larian can expand upon, and I agree they are working on it. The hints are there. A lot of books reference things you encounter in the game. Even Raphael is referenced in a book near Kevlor.

The Arcane Tower was well done on this regard. As was the apothecary. They should do that more often in the game.

Me neither ...
But as far as i know, litteraly everyone can worship any god ... priest, or not priest. O_o

Im just saying that there is other ways to look at this scene.
Maybe your character was so interested in those books, so s/he didnt notice his prayers. :P