magic should be its own thing. if it's possible to use it to do mundane things, it's not really magic anymore, it's basically technology.
and from what i can take from kohaku's contract magic, theres is no stopping it from being a mundane tool. say i have a magic mushroom farming field, and i learned the open contract of tree travel (stepping from one tree to another, kohakus example) there is nothing stopping me from making a magic tree travelling transport system. and this makes magic boring i think. asking the fey creatures for a favor and offering something to magically travel from a tree to another should be a rare thing to happen, not a replacement for a minecart-subway system.
This is what these magic threads keep coming back to, though...
What, exactly are you actually going to do with magic in this game? Are you thinking about how the player interacts with it, really, or are you just thinking about some vague concept of how you think magic "feel"?
Because if it's just how magic should "feel", then I hate to break it to you, but nothing that actually gets programmed is ever going to "feel" as wondrous as you might hope when you are capable of seeing it on a regular basis, and understand the quirks of the system. Again, we
have magic in the game already with vampires, dragons, etc. But they don't
feel all that magical when dragons are just really big creatures with a fire breath special ability that can be hacked down by just a few dwarves with shields.
And you're not going to make anything "more wondrous" again by just making magic random, either. Random events don't inspire wonder, they inspire save-scumming and frustration. They tell players not to bother with the mechanic at all. (How often do you use a Rod of Wonder in D&D when you're not just trying to be an asshole and wreck your friend's game?)
The rules you set guide how the player sees and thinks about the game. Again, I would point to how games like Portal radically change how you see or think about a FPS type of game by simply changing the way your powers work.
So... Why shouldn't magic be mundane?
According to the Threetoe stories, magic
is mundane, especially for elves and wizards.
Threetoe stories pretty much confirm that elves get their wood for trading from singing to the forest to produce wood for them. They use it as a trade good. That's pretty mundane.
The plants that grow underground aren't all mushrooms by any stretch - quarry bushes have leaves and nuts like plants, which really don't sound like mushrooms. Cave wheat is just albino wheat that grows without the sun. That's magic. As is the nether-cap mushroom that magically stays at 0 degrees Celsius at all times. You can make objects from nether-cap wood that maintain that magical property (giving rise to jokes of nether-cap wood boxes being dwarven refrigerators).
That's not even starting with tamable dragons, and having nests of jabberers, and you know those are magic...
Mundane magic isn't just coming, it's already here.
You have to come up with a serious argument for why mundane magic would break down how the player experiences the game to come up with reasons that mundane magic shouldn't be in the game.
Oh, and by the way, if magic isn't mundane, you lose all underground farming that isn't based upon constantly throwing logs/sawdust on wet ground, because anything that isn't a mushroom is magic, and farming is mundane. (Which, again, kind of proves it's all in your head about whether you even recognize something as magic or not...)
Rather than rejecting mundane magic, I think it's better to embrace it.
Elves manufacture all their wooden goods for common trade by using their magic in an industrial manner. The reason they live as they do, so ardently protect their woods the way they do, is because it is the source of their magic, their equivalent of technology. The more pristine and Fairyland-connected their woods are, the more magic floods their woods, and the more that they can use understood, predictable magic to create things of wonder for their daily lives.
They use wood swords because they're magic wood swords, and the power of the spell on those swords is based upon the power of the link to the faerie realm. They eschew metals because it might damage their link to the fae powers they base their culture upon.
Dwarven moods are magic, and produce magic artifacts. Since we farm magic plants, with the proper system in place, you might even have potion-brewing of magic plants, like liquid sunshine from the magical sun berries is right now, or the golden salve...
There's no real way to introduce a wizard's tower eventually without mundanely-used magic like in
Cado, where Cado basically used the light-producing staff that traced how much magic was in the area back to the points that were projecting that magic to produce mundane light whenever he felt like it.
The thing about declaring magic should always be a "gamble" is that any time I hear it, I always wonder if the person saying it doesn't actually mean, "I don't want to use magic, so there should be some reason nobody else does, either."
If dragons have a 1/3 chance of exploding or turning into a fluffy wambler each time they breathe fire, though, how, exactly, will that make them an appropriate challenge? It wouldn't, so you don't want magic random
when it's used against the player, and you don't want random magic when it's just mundane magic mushrooms underground. You only want random magic when it's something the player gets, and you want to keep the game to one where you don't have magic powers at your disposal, (except the ones you already have, like moods and trances and farming underground, because you don't consider those magic, even though they are, just because you already have them,) and that's mostly to keep it out of player hands.
What we really need to do is help blur the lines between what is magic and what is not in this world, so that what we're really dealing with is "this takes up a specific type of energy" and "this works on its own, regardless of the magic field it's in."
Vampires needing a specified amount of blood whose ritual act creates magic for themselves at specific periods of time because they have a magic energy metric that gets depleted (in this case, hijacking the old thirst meter) just by existing, but also allowing for casting magic from this magic energy pool (functionally meaning that they get more thirsty the more they cast magic) allows for this sort of measurable, mundane magic.
You can have semi-White Wolf vampires that can use "Celerity" or something in combat to defeat a siege on their own while at the same time knowing that it will cost you two whole dwarves worth of blood to pay for that. (Where's those haulers that are always on break?...)
In fact, random magic really
cheapens the whole core theme of DF. Magic should serve in the greater purpose of what sort of experience DF as a whole offers players, and as such, shouldn't be something huge and loud and completely overturning everything else that goes on in the game because magic has to be so special. If that means "cheapening magic" in your eyes to keep magic from cheapening the whole game, then it's really worth it, because its the Gestalt of the systems that create the game.
Magic should have at least somewhat predictable effects, or else it ruins the entire play style whereby DF players are forced to be highly cautious and thoughtful, and really understand what it is they are dealing with, unless they want to have some Fun.
That sounds like a
great concept for magic in general, all by itself, but it's not going to happen with random magic, because random magic can't be understood, and being careful doesn't matter.
Instead, you need to have a complex system of costs.
That's what this thread's suggestions try to do - set up the accounting of costs, so that magic can be predictable, but at the same time,
cost something significant enough that it isn't just easy power.
If casting a fireball takes growing a field of magma blooms that require months of tilling and the labor of a dozen dwarves, then even if it's "mundane" and predictable what a fireball will do, it will nevertheless be a rare sight unless you are willing to put up with the costs of doing it.
If those magma blooms don't grow at all without living your life in a specific prescribed way, then it's even more constraining. Consider that the elves live their incredibly restricted lives specifically because of their Nature Spirit - they have to give up metal and stone and anything obtained by killing animals that didn't die natural deaths just to get their magic.
That's a significant cost.