Long-term average stock market return is 5-8% depending on who you ask. So an index fund or balanced fund of funds would yield much better returns than bitcoin.
The (S&P 500) stock market return:
1) Since 1971 (40 years) is roughly 1300%, which is 19.63% annualized (1.1963^40 = 1300).
2) Since 1950 (60 years) is roughly 7680%, which is 16.08% annualized (1.1608^60 = 7680)
That's actually 0.06% per year. I wish it was per week... there was a time when it was over 5%!
Assuming the cost of the electricitiy is 1.26 cents per kwh, and your machine is running at around 800 wats, constantly, that's 720 hours and 576 kwh, seven dollars a month...so the cost of running doesn't seem to be that high either.
Edited for bad math. May continue to do so. Please point out errors.