Turns out that OS X Yosemite on Mac Mini does not support standard Wake-On-Lan (“WOL”), at least not when using the built-in Ethernet port.
Which is strange – but when trying to make the media server attached to the household’s TV a bit more energy efficient, I just couldn’t get that Mac Mini to come out of sleep using a WOL magic packet. Others out there report the same thing, so it’s not an isolated issue for me. Just to rule out issues with the WOL client used, I tried waking Windows and Linux machines from sleep – worked flawlessly. Weird.
There was however an easy workaround: