[Rendar]

Doubling the base spell power and halving the cost of healing spells works just fine.

1.5x after calculation would be kind of ridiculous. (WIL+Pwr+TomePwr)*1.5 heals for... a lot. To much in fact.

I'm going to provide some stats.

70 WIL, 20 power tome, Rank 1 graft.

70+20+2=92*1.5=138 HP for a heal.

for what I suggest, just change it so that their healing spells cost half and still get their current benefit.

70 WIL, 20 power tome, Rank 5 Graft.

70+20+24=114 total and costs skill points. That's pretty balanced to me.