I was thinking about a different take on Reserve Feats. This idea would only work if we assumed 0-level spells could be used at-will (house rules I use). The idea would be to take a feat to beef up one of these spells. It would be less powerful than what you could typically cast at any given level, but it wouldn't use up any of your spells per day.
A second note: I've changed the damage-dealing cantrips to be slightly more powerful. The feats will be based on these versions of the spells:
Acid Splash:
As normal, except the spell deals 1d4 damage per odd caster level (capped at 5d4 at 9th level).
Disrupt Undead:
As normal, except the spell deals 1d10 points of damage per odd caster level (capped at 5d10 at 9th level).
Electric Jolt
As normal, except the spell deals 1d6 damage per odd caster level (capped at 5d6 at 9th level).
Finger of Fire
Evocation [Fire]
(Pyro 0, Sor/Wiz 0)
As Ray of Frost, but fire damage.
Force Bolt
Evocation [Force]
(Sor/Wiz 0)
As Ray of Frost, but force damage and all dice are d3 instead of d6.
Ray of Frost:
As normal, except the spell deals 1d6 damage per odd caster level (capped at 5d6 at 9th level).
Sonic Snap
As normal, except the spell deals 1d3 damage per odd caster level (capped at 5d3 at 9th level). The Will save is replaced with a Fort save, both to negate the deafening effect, and to half the damage.
In addition, Cure/Inflict Minor Wounds only heal targets below half their maximum HP.
So, with that in mind:
Burst of Flame [General]Prerequisite: Able to cast
Finger of Fire. Caster level 3+.
Benefit: When casting
Finger of Fire, instead of making a ranged touch attack, you affect all targets in a five-foot radius. A successful Reflex save halves the damage. In addition, the damage cap for
Finger of Fire is increased to 10d6 at 19th level. Any target that fails its Reflex save and takes damage starts on fire, taking 1d6 fire damage for every 2d6 damage the spell deals (round down). This lasts one round for every 2d6 damage the spell deals (round down), or until the flames are extinguished.
Cone of Frost [General]Prerequisite: Able to cast
Ray of Frost. Caster level 3+.
Benefit: When casting
Ray of Frost change the range to 15 feet plus five feet per three caster levels and the range to a cone of equal size. Instead of making a ranged touch attack, all targets in the area take cold damage, with a Fortitude save halving the damage. In addition, the damage cap for
Ray of Frost is increased to 10d6 at 19th level. Any creature who fails their Fortitude save and takes damage has their speed (all movement modes) halved for one round per caster level. Each creature can only have their speed halved by this effect once at a time, although future uses can extend the duration.
Corrosive Spray [General]Prerequisite: Able to cast
Acid Splash. Caster level 3+.
Benefit: When casting
Acid Splash, if the attack roll succeeds, each creature adjacent to the target suffers one point of acid damage per die of damage dealt to the target. In addition, the damage cap for
Acid Splash is increased to 10d4 at 19th level. If the target takes damage from this spell, any damage reduction it has is reduced by one point per two caster levels (to a minimum of zero) for one round per caster level. Each creature can only have their damage reduction reduced this way once at a time, but additional uses can extend the duration.
Curing Touch [General]Prerequisite: Able to cast
Cure Minor Wounds. Caster level 3+.
Benefit: When casting
Cure Minor Wounds, you heal 1d6 hit points of damage per every odd caster level (2d6 at 3rd level, 3d6 at 5th, etc). You are able to heal targets above half their hit points, but they are only healed one point per every odd level once they are above half.
Cure Minor Wounds always does full damage against creatures damaged by positive energy.
Electric Bolt [General]Prerequisite: Able to cast
Electric Jolt. Caster level 3+.
Benefit: When casting
Electric Jolt, change the area to a line extending out to close range. Instead of making a ranged touch attack, all targets in the area take electricity damage, with a Refelx save halving the damage. In addition, the damage cap for
Electric Jolt is increased to 10d6 at 19th level. Any creature who fails their Reflex save and takes damage is entangled for one round per caster level.
Force Dart [General]Prerequisite: Able to cast
Force Bolt. Caster level 3+.
Benefit: When casting
Force Bolt, you may opt to cast it as a full-round action. When doing so, you may shoot a number of bolts equal to the number of attacks you'd be able to make from your Base Attack Bonus. Each attack requires a separate attack roll, and may affect a different target than previous attacks. You do not get extra attacks from Two Weapon Fighting or Rapid Shot, but you do get an extra attack if affected by
Haste. In addition, the damage cap for
Force Bolt is increased to 10d3 at 19th level.
[General]ThunderclapPrerequisite: Able to cast
Sonic Snap. Caster level 3+.
Benefit: When casting
Sonic Snap, change the area of effect to a five-foot radius. In addition, the damage cap for
Sonic Snap is increased to 10d3 at 19th level. Any creature that fails it's Fortitude save and takes damage is knocked prone (in addition to the normal effect of being deafened).
Touch of Pain [General]Prerequisite: Able to cast
Inflict Minor Wounds. Caster level 3+.
Benefit: When casting
Inflict Minor Wounds, you deal 1d6 hit points of damage per every odd caster level (2d6 at 3rd level, 3d6 at 5th, etc). You are able to heal targets above half their hit points, but they are only healed one point per every odd level once they are above half.
Inflict Minor Wounds always does full damage against creatures damaged by negative energy.
Zone of Disruption [General]Prerequisite: Able to cast
Able to cast Disrupt Undead. Caster level 3+.
Benefit: When casting
Disrupt Undead, instead of making a ranged touch attack, you affect all targets in a five-foot radius. A successful Will save halves the damage. In addition, the damage cap for
Disrupt Undead is increased to 10d10 at 19th level. Any undead creatures damaged by the spell who fail their Will save must flee from the caster for 1d4 rounds in the using the fastest means available. If they cannot flee, they cower for the duration, unless they are approached within 10 feet.