investment is a pretty strong term for what a lot of us did to make money at btc.
I made quite a bit of money by throwing my ex-gaming 4870x2 radeon machine into a closet for a year.
my investment was a few bucks in energy, and an old computer that was going to become e-waste, and a few minutes time.
I got lucky that at the time this was a feasible strategy before ASIC domination -- but this 'investment' wasn't anything like the rest of my portfolio by any means.
Mining can be an investment, if you can stomach the volatility and have a plan to mitigate the risk. But buying a currency with the mere hope that it will go up is just speculation, pure and simple.