Eckhard,
Agree with you comments although I would caution anyone regardless of flight plan construction, to strickly observe the procedures set don in your ops manuals. When one crewmember is off on his own doing his own nav techniques is when one is most likely to encounter an error that leads to something bigger.
Having said that, I also prefere True over Mag for all the reasons stated.
Sacul12,
Not a big deal as it relates to this dicussion but the FAA defines the "Polar Region" as anything above N78. There is another
undefined Area of Magnetic Unreliability, (AMU) in Russian airspace and crews should be aware that when operating in these regions, True headings are applicable and shown as such on the Jepp charts. These areas are in Maggadan airspace as I recall.
Google Advisory Circular AC120-42B, Chapt. 6 along with MNPS manual Edition 8, for more information on both polar and MNPS flight operations. Good stuff if not a little dry.
