Ted, its awesome to see the write up. I’ve been using dnsmasq on a router running TomatoUSB (similar to DD-WRT) to just reroute the traffic to a Raspberry Pi that toggles a light (a la http://timleland.com/wireless-power-outlets/ except using these — http://www.amazon.com/gp/product/B00L1P44R8). $5 wifi/radio light switches, basically.
However, the dnsmasq approach is slow — clicking the dash takes 5–7 seconds to reach the pi. What sort of speed does your approach have? Would the ARP approach save much time? In theory I should be able to build some ESP8266 buttons (a la http://benlo.com/esp8266/esp8266Projects.html#thebutton) which should be about the same cost (in $, not in time) and get the time down to 2 sec or so, but I like the idea of repurposing the Dash Buttons.
Lastly, http://blog.ifttt.com/post/121786069098/introducing-the-maker-channel. It’s still pretty new and doesn’t seem to be widely known about yet, but it really does utterly open up what one can do with these.