increased fuel consumption of spinning down and then spinning back up
wastes a tremendous amount of fuel to spin down/up again
I think a flywheel mechanical energy storage system could both serve as a way to store energy and as a way to manipulate the rotation while preserving rotational energy. To slow down the rotation, transfer the rotational energy to a flywheel, and then transfer it back when you need to go back to speed. That adds some mechanical complexity but it creates a more efficient way to control rotation. Plus with electric motors and solar panels, that should be possible to manage without using any propellant fuel.
I wonder if two opposing rings would be connected by some sort of circular maglev track where the mechanism would just preserve overall angular velocity but spin the two halves in opposite directions. The spin could be entirely powered by electric motors, and energy could be conserved if it needs to slow down or speed up. That might be a lot of mass, but it might not cost any fuel to get it spinning.