I do not think that for bitcoin to become a popular and efficient payment method it needs to be a good store of value, as OP affirms. In fact, in these moments in which the price has found some stability bitcoin is functioning quite competitively as a payment processor, although as is well known still have to make great efforts to make it competitive in situations of maximum demand as the observed at the end of last year, when transactions were very expensive and slow.

And that's why the issue of scalability seems even more important to me than the issue of making bitcoin a reliable store of value.