Perhaps, but frankly if all you do with your mage is cast Heal/Group then there is no way in hell you'd be able to handle it fights. Higher Magic/Spellpower will have an effect on it. But you also need it to make your crowd control/damage spells better.
On a side note, 115 Spellpower = 91 Group Heal, 73 Heal
80 Spellpower = 76 Group Heal, 61 Heal
39 Spellpower = 59 Group Heal, 47 Heal
Admittadly its not much for the huge investment, but the reason your using Heal is to avoid necking loads of Health potions and the difference would add up. The recharge times aren't low enough to make spam better than powerful heals.