Part of the value in collectable cards is that they can be resold. There would be no way to guarantee that any second hand "bitcard" has any funds remaning.
Can't the balance of an address be checked on the blockchain by anyone? I mean that's part of the idea behind this whole bitcoin business as far as I understood. The whole community checks and confirms every transaction and thus also every adresses balance.
That in turn would make any rare second hand card that still has it's BTC avlue intact even more valuable.