I'm not sure now that I want to leave it on 24/7 anyway. The Dick Smith power supply hums a little when it's turned off, so I might want to get a good quality 6V power supply, maybe even one that switches off if there's no current draw.
The way I have it wired I can plug the USB into the power socket and run it from TV power, or run it from a standard 6-12V power source. I have no idea how much current it'd draw from the TV, and I don't have the motivation measure it. It's taken waaaaay more time and effort than I expected!