Personal Thoughts and Feedback On the Gold Items
Let's start off with saying I love the quest system and 650 gold is around the 15 minute mark more/less which is a reasonable time span to get your quest activated.
On an individual note:
~ Ancient Coin Line: Mana coins are weak but getting the coin feels good, the reward does not, gold coins are great and definitely worthy feeling. Mana coins I say make it MAX mana rather than MISSING mana, similar to how Bard chimes games missing mana instead of their current maximum mana (I think Bard chimes also gave 8% missing mana as well when he was first released, those were very lack luster (it might have been 12% missing mana), but once it became 12% max mana which is what is now the reward is definitely there). So buff mana coins to max mana would help bring them up to par to the gold coins, or give mana regen again but the mana coins being stronger would feel better than an ambient mana restoration. Overall the ancient coin line is a much greater improvement over the old coin line and feels fun to use with coin collecting mini game, 9/10.
~ Spell Thief Line: The movement speed is just wrong for support and I don't like it. It kind of feels good, but not for me who has a very team-orientated mindset and wants to help me team out, also movespeed makes no sense with frost queen. I recommend making the quest procs slow the enemy for a short time instead rather than grant yourself movement speed, this will help out you as a ranged mage to kite and help your team out with the bonus CC; and can be a powerful slow because it is not a permanent slow since the charges have a cooldown (powerful as in like 50% for 1.5 seconds for example, nothing like 80% slow or anything around that just to be clear). Also if you are going to nerf the mana regen a compensation of something like charges restore some % max mana instead of bonus damage (or along side bonus damage even) would be nice rather than nerfing mana regen every 6 months.
~ Relic Shield Line: I don't play much tank supports. In short I imagine the quest feels good to work for and achieve like the other two gold items.