Personally, I don't pay attention or appreciate most of the art in RPG books for it to be anything but something that boosts the cost and page count. I like some fantasy art, even some of the cartoon doodles in the DMG, but I'd want them in a poster, not a book. The book for me serves an entirely practical purpose, making the rules available in as concise and convenient a format as possible. My imagination is better than most art, and the art I really like is high-end hyper realistic Osprey art that no OSR company seems able to afford or inclined to produce.Novels do not have any pictures in them, and I have no problem imagining the world depicted therein. Encyclopedias, books on history and philosophy, reference works, etc. rarely have pictures, and when they do, those pictures are diagrams, schematics, maps, illustrative photographs, etc. that depict the subject being discussed, not unrelated and inconsistent pictures of people grimacing or posing while doing things that have no relation to the text.
Art in most game books is bad because it is inconsistent, useless and irrelevant. No art is better than bad art in RPGs, and almost all RPGs have bad art in them.
When I bought Darkest Dungeon and grabbed their free PDF, I wished I'd done the latter first - because as much as I love Dore, Dore has nothing to do with the rules of the game. It does add a lot of black that drives up printing costs, however. I positively prefer the old-style of 0e module which is just pages and pages of text. The formatting could be improved, for readability and so forth - a typewriter is not the ideal word processor - but, unless it's a map or MAYBE a monster illustration, having a picture of some random fantasy snowflake in horrible looking armor doesn't do anything for me. In fact, the character art in AD&D2e is so bad I drew on it in high school - I don't want Grand Heroes who look like 80s Romance novel models, so it's just completely the wrong tone. I have such particular tastes in art (including music) that if it's not something I personally selected I'd probably just as soon not have it.
Art has never had much of anything to do with why I buy RPG books (many of my favorite RPGs are produced on shoestring budgets, anyway, and look it) but if I see a big glossy book with a bunch of full page paintings, I'm definitely not going to buy that. Most RPG books are too large for no good reason, anyway, which is why I prefer PDFs even when I have the books. I can fit every RPG book ever printed in my jacket pocket, why would I need paper? I know some people find paper 'easier to use', but I am an office nerd and have been using computers since I was like 8, so 'search' function is a lot easier and more efficient for me than randomly leafing through pages hoping to find the right section.
I very frequently take the PDFs now (which is what I primarily use) and delete all the art, remove the borders, and republish it that way for my tablet. Easier to navigate, loads faster, takes us much less space on my SD card. The only version of OSE I'm going to use is the text-only version.
The unfortunate part is that the books are already too-elaborately formatted with all kinds of filler backgrounds, side bars and so forth, all positioned around the art, and it still wastes space as a white. But a white space where I can write notes is more useful to me than a picture of a kobold ever has been.
I'm thinking about systematically going through the BFRPG book, stripping all art and reformatting it to A5 for tablet reading, eliminating all the blank spaces and shrinking the font down to size 10 or 11 for the main text (size 12 is already excessive for a screen) and making the entire thing single column. If anyone else prefers these bare-bones, no frills, tablet/computer oriented versions let me know, because I know I wish someone else had already done this stuff for me.