The only energy cost that matters is to the operator. Old hardware costs more to run so why would I run it? That there was energy used to produce the device and the replacement is literally not a factor in the calculation.
you have to go for TCO to justify upgrades. energy alone most of the time doesn't justify replacing old hardware.
factor in space (=rent), age related increase in failure rate (=servicing), computer power needs (=opportunity costs) then together with the energy needs you find good points in time to justify an upgrade.
