bitcoin has been used as speculative investment from the day the first transaction has ever happened. it has been a medium of exchange and store of value even back then in the early days.
Are you sure? The first transaction, AFAIK, was Satoshi sending some coins to Hal Finney for test. I don't think that there was much investment in bitcoin until demand for use as the SilkRoad currency drove the price up.
not to mention that the price was nothing, so at launch bitcoin was only see as currency and nothing only, then when it acquired value, it start to become more investment and less currency
but i think in the future it can maintain a good ratio between the two