There are several other reasons for avoiding polar routes.
The radiation levels are much higher, whilst not a problem on a one off basis you wouldn't want to spend a whole career at high latitudes.
GPS/inertial has solved most of the nav problems but your compasses and magnetic tracks are going to be all over the place making monitoring more difficult.
Some aircraft nav kits are only certificated up to a specific latitude. I presume the manufacturer will sell you an upgrade for a price but I assume more testing and extra cost is involved.