How about a tool in the deckbuilder that shows which cards are still missing in My Precious? And maybe how many as well...
I know you can add the missing cards to the needed folder but just as an info for the specific deck...
Example :
Deck needs 4 {Fog} and 2 {Unsummon}
I click on a button and it then tells me that I still need 3 Fog and 1 Unsummon to complete the deck.
I second this! Could be very useful.