I am still a relative newbie, but I can say that when my wife and I were in Scotland last year, I was interested in getting an "appropriate" kilt, one from my family or at least clan. Most Scots I met said, "why? wear something you like, wear something that looks good".
They didn't seem to attach the importance we do to the tartans. I say wear whatever you like, that you feel you can explain to someone who asks. I have worn the Scottish National as well as my own, and never feel like I am inappropriately attired.

Seosamh