I have the enchantment "weapons and armor can be improved 15% better" on a necklace, blacksmith apron, a ring and a pair of gloves but when i go to improve a weapon or armor, it does the same amount of damage or armor as if i wasn't wearing it. I previously tried doing it with a iron dagger i just made but it did nothing as well.
Then enchantment "can be improved x% better" only affect the upgrade of items at a grindstone, not the creation of it. It will allow you to upgrade the item past your current level of smithing. Example to upgrade to superior, you need 31 smithing points. Enchantment can help you to raise this level.