Bitcoin isn't a stock. Most kinds of assets don't provide dividends or other cashflows -- that is certainly not the only determiner of the value of an asset. It would indeed be a bad idea to construct an investment portfolio out of only Bitcoins and no stocks, but that doesn't mean it is without value (for example, as a monetary technology or an inflation hedge)
> It is not at all clear to me that having more (relatively uninformed) speculators will lead to less volatility for such an instrument.
I am not sure how we can judge the informedness of the speculators or what we are comparing them against. But, each additional speculator improves the informedness of the market overall.