I think Pokemon really did a great job creating these two sets
Adriana, Captain of the Guard
While most people were focused on the Lions Eye Diamonds and Lotus Vales of the world, Flash quietly picked up errata that basically made it so that you couldnt just pick a creature and not pay for it, so that you could do the enters the battlefield trick which was the exact trick the card was originally designed to allow for (albeit, long before they conceived of just how big of design constraints this could put on them in the future if they changed the types of creatures they made)
Its hard to beat the variety that TCGPlayer offers
But if history is any indicator, its possible that this rule could be adopted for all levels of play, so long as the feedback from the players is positive
There are also additional features like holographic accents, collector numbers, and promotional features that compound with a cards rarity and further increase value