No. However, a bit extravagant. Are you thinkg KTM SM coz its got good trip bike potential, or just because I like them?
From Anchorage all the way to Panama, I think you could go paved on the Pan american all the way. Needless to say the SM would be a real pain off-road, unless you are a riding god...Up to you to decide that one! So this would restrict your options, once on the trip. With this in mind I think its worth remembering that with a biking overland trip, the bike should complement the trip, not restrict you unecessarily.
So go for it if you think you'd really enjoy it more with that bike. Otherwise, consider the SM when you get back (a trip like that would obliterate the resale value, IMO), plus you would not have to worry about any warranty claims if you still at home. And for the trip, get a cheaper bike like the popular XTs, KLR, Africa Twins etc. Then you only need save up another £1500-2000 to make the difference and buy a SM on your return...
In short yes you can do it, but would you wish you had something less damamgeable with knobblies and not likely to depreciate once you are out there!
Adventure: it's an experience, not a style!
(so ride what you like, but ride it somewhere new!)