Demand is probably almost entirely speculative, which is nothing new. The Chicago Mercantile Exchange is launching Bitcoin futures in a few weeks, which I think contributes to the current run-up.

Bitcoin is backed by same thing art is: scarcity, durability, transferability. Anything with these qualities will appreciate in value as wealth of civilisation grows.

Penny stocks are also scarce, durable and transferable...

Penny stocks are generally not scarce (You can buy a lot of them) not durable (Companies tend to go bankrupt). Gold would be a better analogy.

People can't create new types of gold by taking an open source coin and forking it...

Gold is only analogous to Bitcoin (or any one specific crypto), not the entire phenomenon. People can create new companies and list their stock but that in itself has no impact on stock prices.

No, but they did attract a new wave of speculators to the ecosystem.

Nothing, the only reason to buy it is that people think they'll be able to sell it to someone else for more later. Other cryptos are way better at actually doing things.