Rewards card value dropping should be expected. Stuff that is given out for free so abundantly won't hold short term value. The founders did say that there is a max supply of these cards but no number was decided on yet. So if all goes well the reward cards won today may be worth more months down the road.

This new system is way better then the last. It provides a way for those who just want to play the game to earn cards for free and the farming of these cards don't hurt the value of the games paid for cards / packs.