After finally knuckling down and asking about getting the minimap texture named in the official forums, I found that someone
<cough> Gello <cough> had beat me to the punch.
http://forums.worldofwarcraft.com/th...n&t=138577&p=3
Looks like all it will take to do a proper reskin of the minimap and the casting bar is a little patience.
EDIT: actually, that thread is chock-o-block with blue text.. lot of nice info there. I linked to page three, but take it from the top. It's a good read.