AND why would you do anything in the first place. If nothing has value, it's free! You can get all the furniture, cars, houses, bits and pieces you like for nothing. Unless, of course, you have to work for it. Which would mean those objects have value.... wait a sec...
Yep. Immediate barter. As George O. Smith put it, "a washed car's worth of dug postholes." Smith realized that there are certain things that people want that can't be duplicated. For example, you may want a house with a gorgeous view of Lake Tahoe, but there is only one house in existence that has that exact view and you want it. You don't want the house next door - it doesn't have quite the same view. So how do you pay for it? @Selbbin, you're right. In a subsequent story, Smith had to have the same engineers who invented the duplicating machine invent something that can't be duplicated - that right there re-establishes a basis for a currency. They ended up with money again. But it was fun while it lasted!
Yes. While the current exchange mechanisms can be duplicated (try quantitative easing!) not everything can be duplicated. You get sick, you need a doctor. You can't duplicate a doctor. You want that house in that exact location, you can't duplicate it. So some form of exchange would need to develop. And how many 'I'll mow your lawn if you cure me of cancer' swaps is the doctor going to be motivated to accept, as payment for his skill and years of study?