I really don't see why cards such as scarecrow and nova and the like shouldn't be enchantable. Sure scarecrow would heal for a lot, but it tends to max out death's health points as it is now and death wouldn't be able to keep any excess health points as any sort of health bonus (healed is healed after all). The nova card of balance school if enchanted wouldn't be out of line with either sandstorm or Ra on a damage per pip bases or even an effect basis as whether to toss an enchanted Ra or an enchanted nova is pretty much a toss up.
Healing cards is another subject, but I still think one should be able to drop strong type cards on heals to increase their effect. As far as satyr goes, I might even be inclined to drop targeting cards onto it as I am quite tired of seeing satyrs fizzle when I need them.
As for scarecrow and nova, i really don' care. Whatever ki sees fit i will go with. As for heals, i would like to see different types of enchants and star spells to boost them.
It would be really nice if Nova's classification would change from Charm to Attack. It doesn't seem right that Nova is a Charm when Efreet, which gives out a more powerful Weakness, is an Attack spell.
Death seems to be the one school that cannot really take advantage of the Sun damage enchantments. Their sole AoE is Scarecrow. As you point out rightly, in most cases, the health-steal goes over the top, so Necromancers don't even get full benefit of the life-stealing. However, if the life-steal is of a concern, how about letting the damage part be enhantable and the life-steal could stay the same or only increase by 2/3 or something like that?
What may be interesting would be a few new series of Enchantment Spells.
The first is a Life School series that increases the amount of Damage Healed; these would be used on Heal Spells.
Next, an Ice School series that increases the amount of Damage a Shield or Damage-reducing Charm (like Weakness) mitigates; for example, an Enchantment that adds 5% to Shields (a FireShield would block 85%). Seeing as the multiple Shields can't have 5% divvied up, rounding would be in order (EtherShield would block 73% per Shield, and ElementalShield would block 52% per Shield).
Finally, a Storm School series would do the opposite of the Ice-School series; it would increase the boost Blades and Traps give.
