I think Jock's piece sums up kilt-wearing in Scotland pretty well in that it is something worn for special occasions - dances, weddings etc. - not an everyday form of dress. And I would be prepared to place a bet that those self-same young people, if they were transported back in time to the 1960's, would have been sporting dinner suits (tuxedos), at least the men would have. Highland dress was quite a rarity when I was growing up, as was dressing up at all in truth. Smart casual was the thing. Then a change came about from the 1980's onward when Scots people began to realise that they were very far from the centre of political power and that their opinions, hopes and aspirations were being ridden roughshod over. Suddenly it became important to assert a Scottish identity to counter this and this took the form of a re-emergence of kilt-wearing, waving the Saltire, singing "Flower of Scotland" and the rise of the SNP as a political force. Whether all of this will seem so important in years to come is debateable but all it needs to ramp it up another level is the election of another alien and unsympathetic government in London.
As to wearing the kilt in the Highlands, this has probably always been common amongst the more well-to-do who could afford the luxury of dressing up clothes whereas the general population would more likely be seen in working clothes, much as in the analogy about the crofter wearing overalls and a flat cap but if he was somewhere more dressy then he would take off the cap.