I had the same dilema, invest in coin or buy GPUs. I decided to buy gpus cos after i pay for them i can still mine if not eth then other coin. If i just invest i can only wait for coin to go up, sell and then what? wait for coin to go down buy again wait to go up... do some day trading.... to me its more like a gamble then steady income... with my few rigs (20gpus) i can get ROI this year if eth goes a bit higher. i target to sell at 500$.