I don't want to be a party pooper but I just want to throw up one bit of cautionary advice.

I agree with everyone here that this event would be a great one to wear a kilt at, however I think the more pressing concern is what your date thinks.

The important thing to remember is that you're trying to impress this girl and as such the night should be about her as much as the concert. I can't see why she wouldn't want you to, but it may depend on how long she's known you etc. Some girls like a confident man, some want a 'normal' man etc.

My advice is to ask your date what she thinks. That will show consideration for her feelings and may earn you brownie points. If she:
A) Never wants you to wear a kilt then you can take that as a bad sign
B) Would like to be more in her comfort zone in these earlier phases of courtship then you can show how warm and caring you are by abiding by that
C) You can rejoice if she thinks it's a cool idea

Hope that helps