Just to throw in my own thoughts on it, since I haven't read any of the books mentioned...
Within certain areas, perhaps you can gain the power of a metamagic feat without actually having it. Or perhaps you can draw on their power to fuel spells, effectively giving you an extra spell slot when within it's power/range. Or maybe it replenishes a spell slot. Or grants you use of a spell.
A couple random ideas...
Cruinn Deann
This ring of stones has four symbols placed on each of the four compass points. Once per day a druid may channel the power of the stones, reducing the casting time of a spell by one round, to a minimum of a one action. This spell must be cast within the circle of stones, at the time of the channeling.
Dawn Barrow
This grave site is the final resting place of an ancient priest of a sun goddess. While within 10' of the barrow, any Good-aligned caster may spontaneously convert spells to healing spells, like a Good Cleric.
Desert's Heart
Said to be the birthplace of a vast desert, this convergence of magical energy allows the use of Energy Substitution (Fire) to all within a 30' radius. Spellcasters that prepare their spells may prepare spells with this feat while within the radius as if they had the feat. Spells prepared in such a manner do not lose the effect of the metamagic enhancement when the radius is left. Spontaneous casters may cast spells as if they had the feat, but do not have the casting time increased.