When faced with the massive amount of wasted processor cycles at home, I decided that the only sane way to go, was to actually cut down on the waste by using lower power processors that cost far less energy to run. In truth, I got a bit more complicated than that, but the essence is, cut the power so that I'm not generating the waste.
Cooling the home office became easier as well, because at one point I was talking with an engineering friend of mine about installing decent air conditioning. Now, I don't need it.
OK, there are occasions when I could do with a sudden burst of processing grunt, but, heck, it is a small price to pay. It's a personal choice.
The rewards of hiring out unused cycles, eating in to bandwidth allowances (as I live in the country with pathetically bad internet) just doesn't even come close to the costs it would take me to earn that reward.
Sorry, but this seti/bitcoin cross just doesn't make any sense to me.