It depends really. It was quite easy to sort out a card for the West Ham match and then I would imagine it is easy to top up (not that I needed to). Once you get over the initial hurdle, then it will be much easier to get tickets. Your card will simply be credited.
I am positive that it won't deter people from going along to a brand new stadium that we have been fighting for. Whether or not, there is a charge for the card is another matter.
I can honestly see no reason or need for a charge if the card is too be used.
I put this Scenario to you -
A team of footballers has a game called off and decide last minute to go to the Brighton game and only half have cards.
Under the card system 5 people wouldnt be able to go and the club loses out on money.