All bikes with carbs will perform a little less well, including the TA, high up.
I've been pretty high in Pakistan and Nepal. I found that there was a definite loss of power, but nothing disasterous. Others have been less effected.
Keep that filter clean (better still, fit a K&N one); take off the rear leftside faring and, if things get too bad, you could drill some holes in the plastic around the filter.
But changing the jets? Hardly worth it, unless you're spending weeks up at that altitude. My only suggestion would be not to go with a GS owner: the gloating about fuel injection will be unbearable.
Around the world 2000-2004, on a 1993 Honda Transalp