From my original posit (though I admit I did not explain very clearly); the magnet can be rotated in any plane either perpendicular to, or at any angular deviation plane from the Sun or the Earth's magnetic fileds. In no case is it possible to measure any reduction in strength of the magnets own field.
I agree that energy is not lost or even measurably being expended, by a permanent magnet - but I do not accept that a potential source of replenishment of energy expended, is actually from the Earth, because of the above statements that would suggest a negative (or positive) resultant in the magnet's field strength should affect the strength of the field and be measurable.
This does not, of course, change the fact that work must be done on the magnet to rotate in the external field. This energy would come from whatever device was used to rotate the magnet.
In fact, technically ``magnetic fields cannot do work''. See here for some technical details, or the wiki for an overview. The fundamental origin of force exerted by a magnetic field is the Lorentz force which is perpendicular to the direction of the magnetic field and therefore the magnetic field cannot do work. Forces between two magnets are complicated to calculate, and are largely based on the curvature of the composite magnetic field, in addition to the field strength.
I would say that you can consider a magnetic field to be doing work in some situations (like two magnets attracted together), and certainly the natural equilibrium of two magnets is an arrangement that minimizes field curvature. Just remember that the strength of a magnetic field at a given point is only one part of the ability of that field to exert a force.