Is it that land is no longer valuable, or because land is increasingly only available to a smaller portion of the population? (I'd need to find some data to back this point up...)
The money simply isn't available anymore for the next round of young families to begin buying property like it was generations ago. This allows land to pool into fewer hands and be less economically available.
Also, I'd argue that since capital is so cheap right now, investors and speculators are looking for new places to invest and hence digital currencies seeing the spike they are.
RE: Bitcoin rises because land is becoming worthless