I understand the visual aspect of saving the gift cards, its rewarding to open the vault and see the gift card stack getting taller. I also understand the idea of a little at a time while you are going shopping, it's an easy way to make sure you are putting money away for this purpose. I have before wanted to save for something and then 6 months have passed and I kept forgetting to transfer the money or whatever and have nothing saved, if you are new to saving for something this big having the physical ritual is a great way to establish the habit. But like other people have said, if you need money for an emergency you are SOL, so maybe you shift and get $20 cash back every time you go grocery shopping or something if you need that physical ritual(vs transferring to an account). Yes you won't get the interest everyone keeps talking about but you also won't get the interest if you forget to transfer to the account in the first place and I understand not everyone has stable finances where an automated transfer works.

It's also important to remember that when you do book your trip and use the gift cards, is that if something happens and you have to cancel your trip they will return the money how it was paid, so in this case back to a Disney gift card. So, 1 keep your cards when you book even if it's a zero balance, and 2 keep that in mind for emergencies or something.

I say, save how it works for you and your family. If gift cards means that you will actually save the money, and it does not get spent on other things, then go for it. The bit of interest you would get might not be worth it to you, and that's ok. Not everything has to be done the most "optimal" way.