Under this paradigm, a library full of spellbooks is like a mink farm or a cattle ranch, with all the associated problems. Spells can accidentally crossbreed, cast themselves (with disastrous results), devour each other, or slowly fade.
Sensible wizards keep a spell on one page of a spellbook and fill the facing page (or several pages) with explanatory notes, warnings, and useful notes.
Spellbooks don't burn. Scrolls burn (that's their job), but spellbooks are written on thick vellum. Powerful spells are trapped in gemstones, lead sheets, or gold wafers. Setting fire to a magical library seems like a great way to ruin a wizard and level their tower, but in practice, it usually just scorches the furniture and irritates the cleaning spirits.
Cascade failures (where one spellbook fails and sets off the next spellbook) are possible, but wizards usually space out critical volumes and insert mundane books, lead buffers, or blocks of wood between active works. Magical librarians would feel at home in a nuclear safety course. Incidentally, a good scroll case is designed to turn an accidental magical explosion into a magical shaped charge. Anything directly in front or behind of the scroll case is going to have a very bad day, but the carrier, protected by the tube, might survive.
Sensible wizards also use early warning systems. These days, industrial wizards buy auto-buzzers and colour-coded charms. In the old days, a stuffed alligator and some special herbs served the same purpose. Any escaped necromantic spells might earth in the alligator instead of in the wizard; some herbs react to spells or ambient magic in unusual ways. Wizard kitsch serves a purpose. If a wizard finds a strange rock that vibrates whenever fire magic is cast, they'll probably stick a bell on it and use it as a paperweight, because you never know.
Books of Theory
The saying goes, "Before Principia Arcana, nothing." Principia changed the world. Old magical theories, no matter how elaborately documented or embellished, were swept into the dustbin of history. A few wizards might keep copies of Druidic Laws or Statgolger's Elements to show their erudition, but they aren't reference works.
The saying continues "After Principia Arcana, a lot of bickering." The core principles of the paradigm are widely understood and rigorously tested. The details, such as the Eightfold Theory and the Problem of Classification of Spells, are hotly contested. Every season sees a fresh fleet of books printed in Endon. Keeping track of their arguments, let alone reading all of them, would take a legion of wizards. Most shrug, pick a few ones with decent titles or reputable authors, read the first few chapters, and leave them to decorate a shelf. Industrial magic requires more than mere theory.
History and PoetryWas Cuthbert Coldhand's sword really "so sharpe it cleft / light itself in twain / and scattered half-rainbows like tears to the ground"? Did wizards of old really raise mountains or cut new paths for rivers? Where are the fabled cities of Ithicon and Luuur, whose sorcerers once ruled the known world? Wizards, in their idle hours, like to paw through volumes of forgotten lore, both for inspiration and for potential clues.
Untranslated works in obscure languages fetch high prices at Endon's auctions. Forging them is a lucrative art.
What Not To Do (And How Not To Do It)Few wizards are willing to admit that they turned 40,000gp of funding into a small lake of sludge, an ocelot that can sing, and a permanent odour of buttermilk. A wizard has to balance the humiliation of publishing their failures with potential gains in revenue, credibility, and survival. The nascent academic publishing system in Endon is more of a newsletter distribution mechanism; wizards publish papers by stuffing notes under doors, taunting rivals, or writing screeds to the editors of papers.
Since spectacular disasters tend to destroy all notes, experimenters, equipment, and witnesses, reconstructing events that lead to the final "hrm, that doesn't look right" moment is a difficult art. Retrograde scrying is possible, but grows increasingly fuzzy near high-powered magic events. Wizards with the skill and experience to examine the wreckage tend to stay away from smouldering craters. The mob might mistake them for the perpetrator. The greater the disaster, the more speculative the reconstruction. Criminal prosecution can uncover all sorts of interesting details. The courts of Endon are notoriously slow, corrupt, and ignorant of magical matters, but when the public good is at stake they can force wizards to explain extremely complex concepts in absurd levels of detail. Court transcripts (copied by diligent scribe-spells) form a solid core of many libraries.
The line between "cautionary tale" and "instruction manual" is very thin. One wizard's disaster might be another wizard's desired outcome.
Bottled MemoirsWizards with more money than sense buy and store bottled memories. Drink one and you gain a new memory. If the seller was honest, it might be a titillating, scandalous, or thrilling memory.
Memories are fickle things. Without links to other cues, a new memory fades quickly. It's not an immersive experience (despite promises on the bottles). It's a memory; it's in the past, and all the irrelevant details are fuzzy. Drink too many and your own memories will get mixed up.
Some wizards are said to store crucial trade secrets in memory bottles, but it's a device from melodrama, not from life. The safest and most useful place for a secret is in the wizard's head.
More than one wizard, haunted by youthful hubris or foolish decisions (the kind that arrive suddenly in the night and make one want to gouge out one's forehead with a metal brush), has prised offending memories out of their head and stuffed them into bottles, to be stored and ignored. Editing your own past is a recipe for disaster; your past mistakes inform your present self. Still, it's a tempting prospect. Woe betide the burglar who downs a draught labelled "A Night With A Princess of Thule" and gets a brainful of "My First Date And The Horrible Aftermath", courtesy of a frugal wizard reusing bottles.
Extracting a recent memory from a trained and willing individual requires a trivial spell. Extracting a buried, distant, or complex memory requires a dangerous and experimental helmet, the services of a dubious physician, a human-sized centrifuge (#41 in the catalogue), and some bottled lightning.
Animated PornographyThe oldest enchanted illustration known to Loxdon College features, according to the prudish catalogue card, "two nude figures encountering difficulties while attempting to fold a bearskin rug". Chronoscrying puts the illustration's age after the invention of fire but well before the invention of trousers. Students, of course, use "encountering difficulties" and "folding a bearskin rug" as euphemisms.
Moving illustrations of every act imaginable (and some you can't imagine, even with the aid of explanatory diagrams) are available in Endon for the right price. Owning them is technically a Moral Crime, but punishment (if any) depends on the nature of the acts illustrated, and the outrage that can be mustered locally.
The largest enchanted illustration known to Loxdon College (though not officially) is "Custard Accident #4", a 12'x'18 canvas currently in possession of an anonymous coal magnate.
Book Lists and Useful Tools
I was going to write my own table of books, but a) there are plenty of tables and generators out there, b) MIR has an abundance of name tables, c) the course list in this post can double as reference book titles, and d) the temptation to make them all puns was too high.
Elfmaids and Octopi
1d100 Books Found In A Dungeon
1d100 Worst Books In The World
1d100 Blasphemous Books of the Black Library
1d100 Books of Shadel Port