All this complexity to save a few bucks per year on your electricity bill? This is ridiculous, the Pi costs far more than what you can be expected to save.
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(For example, imagine a big home GPU server that is needed only intermittently, and you want it to spin up automatically on network traffic from family's various devices that you can't modify.)
Of course, if you have simpler needs, and you're willing to send a WOL magic packet from the using devices, you can do in a few lines of shell script. It's a 1-line ssh-to-something-that-can-etherwake-on-that-vlan script, then wait in a loop for the service you need to appear, then 1-line ssh-to-server-to-shutdown when you're done.