As far as broadening the kerning on mountain range labels - one reason to do so is so the label 'claims' all the applicable territory. Same principle as for a river - if it's potentially unclear past a branch what name applies, one either repeats the right one, or spreads out the name till it adjoins both possible portions. I think that's why the best practice for area labels too is to stretch across the whole width of a territory or object, where possible.
When spacing out letters looks too disjointed, one could consider also putting even more space between words. And if even that lets a reader lose track of what's being said, one could switch mountain labeling (unfortunately - all mountain range labeling) to a slightly different font. You're using that nice centered-small-caps variant for multiple extents - territory, bodies of water, AND ranges. Maybe for the ranges you could use an extended font instead. If there isn't one in the font face you've chosen, you could make the tough choice to stretch the one you've got - I know meddling with character proportions is chancy, but the end result might justify it, IF the font is amenable to lengthwise stretching. Incidentally, since stretching larger can lose resolution, maybe the actual process would be to lay out a really big point size and then scrunch it a bit vertically.
I think the kerned versions you show are fine. I kind of expect to do a little hunting to track down long labels. As for the rest of the map - it's made out of Awesome, bolted together with Amazing, and polished with Wonderful. Easily one of the maps I would most like to pore over ... and I have :-).
And thanks to both Raptori and Caenwyr for the demographic resources - great stuff, that!