Spend the extra $200 and you'll won't have to upgrade because you ran out of space.
Or, spend the extra $200, and next year when a 128GB model and maybe a 256GB model are available, you'll sell your 64gb without getting the full $200 back and upgrade, regardless. 64gb is not enough space for any kind of packrat/everything in my library approach. It's just more space than the other current options.
I also think people who believe everyone is going to want 40 movies on their iPads are not thinking about the device as most people will use it. The world contains all kinds of people, and some of them are pack rats who worry about hypothetical situations in which they're in a doctor's waiting room and suddenly have an urgent need to watch Ghostbusters III.