Joe, the only reason that the price of cloud storage would fall is if demand for cloud storage falls. The value of cloud storage over time should be fairly stable, perhaps not as stable as today's US dollar but certainly more stable than bitcoin is today.
But in the case of tulips, bitcoins, etc., their stability was only derived from their speculative value. Bread will be reasonable stable, because people don't speculate in bread. Bread has a minimum price, because there is a limited supply and a clearly defined need. All commodities are not equal. Bitcoin is one of the worst I can imagine, but the tulips during tulipmania take the cake.
I believe you can regulate cloud storage in a way that prevents fraudsters from manipulating it. The only assumption I need is that the majority of the network is honest. You can use hashing + random strings to confirm that a person still has the file they are hosting. You only need then to be sure that the person hosting the file and the person uploading the file are not in cahoots. You can achieve that by making a random mapping between people and hosts, and only picking the host after a person has announced how much file storage they wish to rent (and paid for the first month). This makes it too expensive to host files on your own machines, because you have a very low probability of getting the opportunity to store a file on your own machine.