The smaller the displacement, the more susceptible to altitude/temp changes they are. My 500 runs the same at 3000ft as it does 8000ft, but on my brother's 200 you can feel the power loss at that altitude. One little adjustment on the screw and possibly a needle clip change, and he's back to perfect. Jetting on the trail is no big deal.
It really comes down to where and when you are riding. If you don't change 4000ft of elevation, I couldn't imagine a scenario where changing the jetting would matter one bit. If it's not down on power through the ass-dyno, then just ride that bitch. When you run into a problem, we'll set you straight on jetting. -BIG DAN