Well, as long as I'm covering all the bases, I might as well delve into the concept of magic in the RPG into the bargain.
The "Vancian" magic system, so well-known to A/D&D players, was of course the staple up until the most recent version of the game. And players, on the whole, hated it. Why? Because it limited their characters, of course. Other games worked with other systems. Spell points were the most-seen option on the other end of the spectrum. Where the Vancian system said you could only cram a given number of spells into your brain, and those spells had to be pre-selected, the spell point system pretty much agreed with the basic idea that magic was somehow limited. It simply did away with the idea that the spells needed to be pre-memorized. If you had enough "mana" (or whatever), you could call upon the arcane energies and *BOMF* goes the spell.
Gary Gygax once famously quipped that he had never seen a modern practitioner of magic be so much as able as to cast a first-level magic-user spell (to which I might reply that I've never heard of any priest being able to so much as pray to receive the effect of a first-level cleric spell outside of a charlatan at a tent revival, but I digress). It's a fair point, as far as it goes, but I think the "real world" system of ceremonial magic (and other forms of magic from classical, Medieval, and other periods) might actually be able to be used to form a workable system for a fantasy RPG. I do want the thing to be more rooted in folklore, and magic is a big part of that tradition.
How does European folklore deal with magic? Before the ascension of Christianity, magic was a part of everyday life. Necromancy was well-known to the Greeks and Romans. Romans would put little spells onto pieces of lead sheeting, and stuff them into graves, asking the dead to intervene on their behalf (some graves were even specifically designed to accommodate such work, complete with tubes to accept the prayer-sheets). The Germans had their runes, which were more than mere letters, but a whole esoteric key of magical practices. Charms and spells abound from early Medieval Europe, and the whole realm of fairy-lore could be considered a branch of magic, involved in beseeching the Hidden Folk to grant boons for onesself, or curses on one's enemies. Ceremonial magic dealt with summoning angels and demons through elaborate conjurations based, supposedly, on the work of Moses, Solomon, Hermes (whence the name "Hermetics"), or other famous magi from history. England had its cunning men, and witches were known throughout Europe. And alchemy. The Norse had their rune masters and their seid-workers. And in all cases, we have at least the broad outline of how their magical practices operated. Whether or not you believe it actually worked (or works), what a fruitful field from which to draw ideas!
I like Vancian magic. I think it has a vital role to play in game balance, offering a break on the power of the wizard vis-a-vis other character classes (or, in a skills-based system, those characters who choose skills related to magic-use). But based on my knowledge and studies of how "magic" works and worked in the real-world, I'm not going to be using it.
That said, I'm not going to be using any sort of "spell point" system, either. I find neither the Vancian "the mystic energies imprint themselves on my brain, and are let loose at a moment of my choosing" nor the spell-points-based "I have a limited amount of magical energy to expend in a given time period, and each time I cast a spell it diminishes that supply" to work for my conception of how magic was conceived to work in the ancient, medieval, and Renaissance worlds. How about just "if you know how to do a thing, you can do a thing." Magic as cause-and-effect, just as sure and true as swinging a sword or riding a horse. Can it be done without ruining game balance?
And that's the whole key to such a scheme. If anyone can get a bonus to attack by carving a tyr-rune on their sword, eventually everyone will know the trick and everyone will do it. If everyone with access to the Black Book of Cyprianus can summon a demon or ensure a successful hunt, how could it help but become ubiquitous? In the sense of the campaign setting, it could be done through cultural mores, but player characters are famed far and wide for not paying too much attention to such things, unless there's a real penalty (in game terms) for doing so. Game balance isn't about non-player characters in the setting; it's about players out to (legitimately) try to make their characters as successful as possible.
There is also the question of types of magic. Who's to say that all different types of magic always work the same way? Ceremonial magic, as presented historically, is really pretty dull, time-intensive, and nit-picky. Spending nine months crafting your "tools of arte" to cast a particular spell is hardly a riveting gaming experience. Rune magic, on the other hand, as given in the Icelandic Sagas, can be quite dynamic. You carve a few staves on a piece of wood, touch it to the target (or contrive to get him to touch it) and voila! But the effects are usually subtle. No lightning bolts. No holes opening in the ground to swallow up an opponent. (Although there is a tradition of literal shape-changing.) Charms are just sung or spoken, and the effect is supposed to be immediate. And any peasant's son would know a couple of efficacious charms. No need to spend years studying under some hedge-witch. How would that translate into a game?
I don't claim to have all the answers yet, but it does seem doable.
Maybe the Vancian aspect of preparing spells beforehand could be done with some sort of talismanic system (as mentioned above in connection with the runes). The mage prepares the talismans, and then unleashes them as needed. But how to keep the talisman-maker from just making thousands of them, sort of the equivalent of an old-time D&D character having a golf bag full of wands, staves, and rods? Ease of access? You can only keep track of so many talismans for so many situations? ("Where did I put that 'blast goblins into flinders' amulet? Damnit, no! That's the 'breathe underwater' amulet!") Hmmm... wouldn't THAT be an interesting mechanic? Prepare as many spells as you want. Just try to find them under pressure...
The same would work for potions, of course (or, potions could operate the same way, mechanically, sort of like how they work on "Charmed"; you smash the potion, and the effect happens).
And bear in mind, just because someone puts a cake on the plough and carries it around the field, didn't guarantee there'd be a good harvest in the coming season.