Hello.
Another suggestion about a thing I completely forgot was in the original game:
Tome Decks
Those were paid for with BFP but removed from the game after some time and not useable with your normal collection.
These could reduce the amount of BFP in the game, prevent more cards from entering the game, and make for a challenging and exciting game mode, where even new players without large collections can participate.
Greetings
I'm a new player myself and I can't say anything about former prices.
But as far as I can tell, boosters already make for the best BFP-sink. The BFP used to buy them is completely out of the game.
If older players would receive less or no boosters from quests then they would be more incentivised to buy boosters again or buy cards from other players who in turn use the money to buy boosters.
This way increasing the amount of BFP leaving the came and reducing the rate at wich new cards enter the game. Effectively reducing the rate of devaluation for both.