You don't mine GRC. You crunch science on BOINC. GRC is just a gift. Try to think of it that way instead.

How can I justify running BOINC? Do you care about any of the BOINC projects? That's your justification. You can help find a cure to childhood cancer or HIV, map the galaxy, do really complex math, or several other things. If contributing your compute power to such tasks is not what interests you, then have your machine do something else.

GRC is nothing (literally) without BOINC. If you don't wand to run BOINC, don't consider GRC. But if you love BOINC and all that it can do, then the Gridcoin community would love to have you back on board.