Make it so there is a way to toggle the shop to hide items you already have from the event. Like if someone wants to have all of the items once, they could push a button that would hide what they already have and show what they don't have from the event shop. I know that if this button got added it would be a lot easier for us players who are on a quest to be every item at least once. The button could work the like Hide Event Activity button where you can turn it on and off as much as you like. So that if someone wanted to get everything once first they could turn it on and then if they wanted more stuff they could just turn it off whenever they want. It wouldn't be permanent and you can turn it off and on as you need to.
Feel free to comment on any ideas that could be added for this or to make it better.