In an economic sense,
An INVESTMENT is the purchase of goods that are not consumed today but are used in the future to create wealth.
In finance
An INVESTMENT is a monetary asset purchased with the idea that the asset will provide income in the future or will later be sold at a higher price for a profit.
I really don't want to turn these into an economics class but the both definition of what investments are clearly should settle the argument of whether BTC is truly an investment or not.
I think this depends on your perception of bitcoin, investment or trading. because after all there will be many debates that will never run out. the basic concept is virtual currency. but bitcoin can be a promising investment in the future.
so I think choose the one that suits you.
As of now it is more on investment because it is more profitable. Others people compared bitcoin in gold and silver because of the higher value in our market. But some other countries start to avcepted as a payment system, a fit for the defination.