"Spell Damage is an ability which boosts the overall damage of spells by the listed amount". So, each spell have its base damage + the possible spell damage increased by other cards that have been played. If you lose the resource that gives you spell damage, you lose it.
So base damage and spell damage are clearly separated. It'll add 1 more damage to the base version.
this will end fatigue for mage.. i think this card is dangerous
This! I love mage but it was too OP before this, now every single deck will run this and there is no answer to it except deck burn unless your running paladin/mage with their secrets teched in. The 2 cost makes it hard to trap ignite with secrets though... Change ignite so the cost goes up by 2 each time and it will be more balanced.