I've been thinking about spell points for A/X. Originally I was thinking of rolling the resource model for spells all the way back to "spells are per adventure", but 1) this is a somewhat dissociated resource model which would require in-world explanation and induces weird edge cases around "well what's an adventure", and 2) I'm thinking that if HP and mercenaries can be recovered (slowly) in the wilderness in refuges, perhaps it makes sense for magic to also be recoverable in the wilderness (slowly). But spell slots of particular levels are very quantized; doing slow recovery without breaking them up sounds like it would end up being complicated.
At 1d3 HP per day of bed rest in reasonably sanitary conditions, an average first-level fighter can recover full HP in about two days. So putting magic at parity, it would make sense for the average first-level mage to be able to recover a first level spell about every two days. This means first level spells need to cost more than one spell point - two seems workable.
This got me thinking also - most spell point systems make 2nd level spells cost 3, 3rd level spells cost 3, 4th 7, 5th 9. This is pretty close to reasonable except at the very low end. Is web really worth three castings of sleep? Is fireball worth five castings of sleep? I tend to think not really, with OSR sleep - a fireball wins a wilderness encounter with a band of beastmen by cooking their chieftain, two or three sleeps win an encounter with beastmen by knocking our the chieftain and a couple of gangs. The main thing these higher-level spells have going for them is action economy. So thinking about these factors, 1st level spells costing 2 points and the relationship in power between spells of various levels, I ended up at the Fibonacci sequence.
Spell level: spell points
A fireball once every five days is also pretty close to the recovery time for a badly-injured retinue unit (or for the beastmen you fireballed last week to recover from their burns), which suggests that it's about right for recovery of wilderness-level abilities.
If NPCs follow the same rules, what does this do to the economics of hired spellcasters?
What does this do to the availability of Restore Life and Limb?
Can you recover spell points faster while resting in civilization, where you have all your incense and pentagrams in order beforehand? Can you apply these same sort of things (building sanctuaries, consecrating altars) to improve refuges and boost spell point recovery there?
What of the Contemplation proficiency?
Mercenaries only recover partway (the dead don't rise, but the injured heal) - should there be some analog to that?
Maintaining indefinite-duration spells like continual light and wizard lock - reduce your max spell points?
Places of Power seem like a much more natural fit for spell point systems than for vancian casting - reservoirs of spell points that can be drained but recover slowly.
Are there known pitfalls to spell-point systems that I should be wary of?