Graham, you've got one of the greatest lenses ever produced. Don't second guess that. It is a truely outstanding thing!!
You've got to let go some of your hesitations/questions/concerns. You have a camera and a lens. Just go make some images and deal with the consequences. You have just the same chance of getting it right as you do in getting it wrong, so why worry?
As for coverage? Who cares whether you will ever use it all? Not only is it nice to know it's there if you ever need it, it should give you peace of mind knowing that it is there thanks to the technology that's gone into the design, and that the other lenses around this Focal length have close to the same coverage (115mm Grandagon, 120mm Super Angulon and 120mm Nikkor).