I'm sure this thread spawned from the Moonlet Earring appearing on the cash shop. Thing that makes the Moonlet Earring different from the Minstrel Goobbue is it's means of obtainment. The Moonlet Earring was an event reward, to celebrate(?) the start of the Dalamud storyline. The Minstrel Goobbue was a genuine side-quest, whose rewards weren't in celebration of anything, it was just a side-quest. As such, it wasn't tied to any event, even though it did receive advertising unheard of for any side-quests before nor since that didn't involve Hildibrand. So far Square hasn't made a single non-event side-quest reward available on the cash shop, not even the Hildibrand or Trail of the Twelve rewards. I personally think the the Sylph Goobbue is a perfectly good substitute. As for the 'older one is taller, it's not. Not anymore, anyway, as the Sylph Goobbue is literally just a reskin.