Blizzard recently announced that some cards from the Classic set will go into what they call the Hall of Fame once the new expansion comes out. Cards in the Hall of Fame can't be used in Standard decks. These includes the following neutral cards:
-Sylvanas the Windrunner -Ragnaros Firelord -Azure Drake
and the following class cards:
-Power Overwhelming (Warlock) -Conceal (Rogue) -Ice Lance (Mage)
Blizzard will be offering a pretty substantial dust compensation to balance the loss of those cards. We will get a full dust refund (without having to disenchant) for each of those cards that we own, up to the number you can put in a deck (two for all except for Legendary, one for Legendary)
It is my understanding that they will consider Golden cards first.
Is it worth it then, if you don't already have them golden, to craft a golden copy of Sylvanas and Rag as well as two golden copies of all the other Hall of Fame cards?