I made these statements on the basis of what I did in my Mini (Mk 1 install)

And for the Mark1, your statements were correct. The Mark1 had only a single power connector, meant to be connected to the ignition-switched power. It was the main power feed and responsible for all the juice going to the player.

now how the heck am I going to sort out a decent permanent 12V feed without bodging the harness around, dammit!

If you are not having any problems with your existing installation, then I would suggest that you don't change a thing. If it works, don't fix it.