First of all, it is not really from space. It is not like they are taking the postcards and bringing them to space or printing in orbit. What they will do is fly a weather balloon that will take photos and then make print postcards (on Earth) using the photos they will have taken. I don’t really see the difference between this and taking any NASA or existing satellite photos, making postcards with them and selling them. Also considering the complexity of launching weather balloons, 7,810$ USD seems like a small amount.
Anyway, personally I don’t really see the logic, originality or uniqueness of the project. However, these photos if ever taken, would be rather unique and so would be your postcards. That is probably the only advantage I can see for backing this project. I wish them luck, they have, 25 days to go and they have always raised more than half their pledge goal. So probably it is just me and my, keep it stupid and simple approach.