Hands up every man who argued with his wife over the wedding and then had a successful marriage!

The two most important words in a husband's vocabulary: "Yes, dear."

Seriously:

1. Rex is a genius. Rex is smooth. Rex is a smooth genius.
2. Tell her that you want to look your best, but that she will inevitably look better.
3. Ask her to look ahead twenty years to looking back 19 years. Doesn't she want to remember you looking your best on her wedding day?

While I don't buy the "it's her day" argument, in the end, kilts are just clothes, as you say. If you defer to her in this (without negotiation), you may be displaying great character. If you defer to her in everything, I would not call that healthy.