A few things I think could make this go from a 4 to a 5 are adding a "NEW" mark when you pull something you don't have, an actual numbered list in the sets to see the missing spots of your collections, and perhaps an actual incentive to ranking up your badge for each set
If you play mono-colored decks, you can simply slap 24 lands of that same color in your deck with no worries
I love this sort of mechanic, personally, as it organically energizes itself as the game continues and can be kickstarted if you build around it
As the Cabarettis are high-class fancy party people, the deck focuses on summoning plenty weaker Citizen token creatures to the battlefield in order to really get the party started
Then the ecstatic, addicting hit of finding a rare card washes over me as I pull out some beautifully illustrated Charizard card, and the craving to open a new pack starts all over again