BTC's value is solely based on what you can get with it. It doesn't have much backing it, which is right now the value is just speculation by early adopters and investors. Silk Road was backing up BTC's value (illegally of course) but it was something that made use of BTC to a lot of people. Value won't have anything to do with rarity. Gold's valuable because, like any precious metal, it has uses in chemistry, has various applications, in addition to rarity. BTC doesn't have any use besides what others decide to give to it.