A smaller unit for sparks of life would go like this.
1 Spark of life = 2-4 of the new unit.
2-4 Units = Revive Self
1 Unit = revive other party member with 50%-100% Health.
The reason that it would take less units to revive someone else is because it's like the health-sharing.
Not that thought out of a suggestion... but it's an idea.
I've come up with the idea of a new rarity called a "Life Essence".
TL;DR-or-want-to-click-link - make new sparks of life that can only be used on teammates and make them more common than current sparks and make sparks less common.