John makes a very good point. Jock, you say that despite your Viking ancestors you don't "dress up like a Viking," so why should those with Scottish ancestry want to "dress up like a Scot?"

John's answer gets it right. Because the kilt is clothing, not costume. Those who put on the kilt because they want to "dress up like a Scot" are often the ones that do a serious disservice to the tradition of Highland dress when they do so. Because they view it as a fun costume and not a particular mode of dress with a long and noble tradition -- one that, unlike Viking garb, is still modern and contemporary.

So when I, and others outwith Scotland, put on the kilt, we are not "dressing up as" anything. We are simply ourselves, wearing Scottish National Dress -- and proud of it! :-)