Well, that's about when enchanted items are actually worth using, but to raise the skill you should enchant
everything. Unlike smithing and alchemy, the skill raise amount does not depend on the value of the item you create, but is a flat raise for every enchant. So any jewelry or equipment you don't need? Put the 1% improved something with a petty soul gem on them before selling them. Because just like other crafting skills, maxing it out does break them game
And yes, save Grand and Black soul gems for when your skill is higher.
For me petty and small are for raising the skill, common is for recharging weapons and greater and grand are for making things i actually use.