Not related to the technical aspect,but I don't think spinning the minimap is a good idea.
The minimap helps the player locating himself, like "I know the entrance I need is in the top left part of this area". If you keep spinning the minimap, the player will lose the reference and the minimap will have no purpose other than showing things smaller.
In my opinion, if you're making a radar or something like that, it might make sense to spin it. But not a minimap.
I don't agree with you. Say you are at 0, 0, 0 and you go straight ahead, then your movements are in sync with those of the minimap. Now lets say you turn left and go straight. To the player, it seems you are moving straight, though the dot on the minimap will be going left.