In the thread on sumoned creatures Ars Magica, a paper and pencil RPG, was brought up. I'm a preposterously devoted fan of the game but paper and pencil RPG's (or as many of us like to call them, real RPGs) are drastically different things than turn based strategy games.
However there is one concept from Ars magica that I would like to offer for discussion, that is the concept of Mystery initiation.
In Ars magica characters start with a collection of peculiarities in their magic - a penalty with fire magic, a fantastic ability to cast spells on mice, a cyclical bonus or penalty to their rolls in acordance to the phase of the moon, the ability to incorporate sympathetic bonuses from props and focuses to their magic when casting weather spells, smaller penalties to cast spells while speaking quitely, inability to use magic while in shadows, and so on.
For the most part these virtues and flaws are fixed at character creation and don't often change. The method for changing them is mystery initiation.
Mystery initiation uses quests, rituals and sacrifices to give the character new virtues and flaws. For instance a character who is initiating into the virtue of Arcadian travel must on a specific night starting at a specific location travel without the use of spells deep into the realm of the faerie while being pursued by the inhabitats of the realm. This experience grants the character the arcadian travel ability but it also gives him a phobia appropriate to his pursuers and makes his starting location a permanent arcane connectin to him (that's a big vunerability).
In another example a character who is learning a virtue that allows him the ability to see all sorts of mystical effects and immaterial creatures without needing the use of spells spends three months entombed in a specific dark cave drinking only water and eating only the blandest gruel.
Now while the specific instances can't be tranported into Elemental some basic ideas could be:
1 Gaining characteristics such the abilities in Age of Wonders 2 or Master of Magic - such as alchemist or channeler could be done OUTSIDE of the normal advancement system by the use of quests. (ie. spend four turns in the volcano of Sulpher fissure standing agains the inhabitants until two new moons have crossed the sky),
2 The aquisition of new characeristic past character creation involves difficult choices - sure learning the mystery of Hermetic Glamour magic would rock but do I have the time to devote to it and can I handle the vunerable magic flaw that comes with it?
This system works in Ars magica because the advancement system is inextricably linked to the passage of time, a season spent studying cult lore that is useless outside of intiations is a season not spent studying arts, learning spells, gathering magical resources or enchanting devices. In a TBS game the profit and loss dynamics will probably need to be re-tweaked.