This sounds a bit too Dwarf-Mode centric. If you are making an object that affects a site, you make all sort of Adventure mode and modded edge cases that are really confusing. Does the adventurere gain these abilities as soon as he enters the map? Do tavern visitors gain these abilities while on the map? What about multiple factions operating out of the same site, are all factions buffed/nerfed?
I sort of like the idea, but if it creates a written object it should affect the creatures that read the writing. Cursed writings could cut an attribute in half, or cause a transformation to a night creature, or remove that creatures's ability to read (or learn), etc. While good writings could make them occasionally or always double the output of some reaction, or not use up potash while fertilizing, or raise the reader to accomplished in the related skill, or increase one of their gaits, or grant immunity to fear (or dizzyness), etc.
Magic writings of that sort should be doable just with DFHack and a mod. I don't know if I could make the new mood types/triggers, but all the effects I described could be handled with the eventful plugin and checking the knowledges a creature has for the magic writings. I am a little tempted to try my hand at a script which makes all masterwork writings magical in this way. Stupidly overpowered with just masterwork, should be artifact level power, and probably a performance nightmare, but would make scholars actually useful.
I said it grants the effect passively, because there currently isn't really a way to force a dwarf to read something you want them too.
The books should obviously work like necromancer slabs already do, but that would make them really clunky to use in Fortress mode.
If you have a book that improves the smelting of steel, you would really want all your furnace duty dwarves to have read it, but currently there's not really a good way to enforce that.
Likewise, forcing your fortress to hold it, opens up the problem of having it be stolen, and thus you losing out on its effects.
I like the idea of making it affect attributes, don't know why I haven't thought of that.
I like the idea of Strange Ideas for books. I'm not into books providing upgrades. It feels too techy like an RTS or 4X game.
I don't necessarily agree. Magical books, including ones that provide benefits to the player/hero, have been a staple of fantasy games and literature for generations. The suggestion seems to be in keeping with that tradition to me, and not terribly out-of-place.
Anyway, +1 to this idea as a whole.
Techs in RTS or 4X games are usually not random, while the results of strange ideas very much are (similar to strange moods). Sure they are "upgrades", but you can't force them any easier than you can force artefacts, and perhaps the best way to acquire them might be to steal any that have been created during worldgen.
I also like this idea, especially producing books that have magical effects. However, it should be worked into the myth and magic system whenever that happens, and be unavailable to worlds without magic, or only available through divine inspiration in worlds where mortals don't have access to magic without divine aide (such as current vanilla dwarf fortress)
The cursed knowledge part, I don't really like the idea of it directly worsening reactions/tasks dwarves do regularly, but producing a book that grants random, possibly dangerous powers or effects to those who read it would be cool.
Since the Strange Ideas system is intended to be a sister system to Strange Moods, it's existence in a world should be tied to Strange moods. Mundane ideas are supposed to be the simplest/weakest/least magical of the bunch, while Blessed ones are the direct counterpart to Possessed Moods, and thus also granted by a divine will.
Personally I like the idea of cursed knowledge sitting like a virus in your dwarves mind, making them just a tad bit worse.
It adds another element that could doom your fort, that isn't directly tied to invaders killing your dwarves.