Gold has an inherit store of value.
Bitcoins have value because you can buy stuff with them and they now have a track record of enabling both on and off the record 'fiscal' transactions.
Finding cunningham chains for fun while generating primecoins as a by product does not produce a *demand* to purchase coins- which is what is required to drive price - but merely increases *supply*.
Gold's "inherit store of value" is no different than any of the cryptocurrency. It has longer history, more fans, but essentially the same kind of value. You can't produce gold at will, it almost never changes. These are exactly the reason people trust gold to be a proof of value. For a well designed cryptocurrency, as long as you can't produce or replicate it at will, it could serve the same purpose.