The machine was future e-waste since it was produced. That is a sunken environmental cost and shouldn't figure into the equation of whether it is useful to prolong its life. There is a running environmental impact related to power usage. This is the one that you need to offset with gained utility. But perhaps the most important decision: at this point you are in control of the end-of-life handling. You can opt for the most responsible process. Once you donate or sell the machine, you have no control, and the further down it goes the more chance it will end up in an illegal landfill, or in a Chinese toxic child-labour scavenging yard.