I personally think this pay by credit or debt card is only hurting them. Think about it, JW's do everything to impress others. I remember a few waving around their checks as the walked slowly toward the donation box, hoping everyone would notice. I'm going to guess if no one is watching them they would choose to use their hard earned money in other ways.
The contribution boxes are still there for the ones who like to show off. Meanwhile, the forgetful ones will probably end up paying more if it's automatic.
The only way I see it hurting them is for people like me who see all the wasteful spending on poinless renovations and spending $100k+ on computers/projectors/TVs for the assembly halls, etc, then watch as they add credit card and ATM machines to the assembly halls and conventions after years of railing on "christendom" for doing the same. For me it was: wasteful spending + trying to get more donations = i'm cutting you off.
Folks that see the pattern and recognize it for what it is are probably a very very small minority, so the net effect of this is that they'll keep raking it in. There's a limit to how much juice you can get from the orange, and I think they're coming up on it soon. People can only give so much with nothing in return.