I would guess somewhere like Iceland the biggest tyre challenge is rocky roads and the danger of side wall splits? In which case the XZY is a darned good choice. Or, as Jasper is already in Aberdeen (so very little asphalt to Iceland!) how about some super rugged (and cheap) cross-ply tyres? Of course they will no doubt be even worse than an XZY to lever off a rim!
But yes, I would take a second spare or tyre (assuming you have the gear to change it onto a rim). For the price of a rim and tyre from Vass I would go for it.
(cheap Nescafe at this time!)