A good question Jock. I have been to 2 white tie events in my life ( I am over 50) and they were before I was kilted. Both were police events and naturally I wore police mess dress. (very much the same as military mess dress)

I have been to a number of Highland balls and other functions in Australia (black tie events) and have rarely seen fly plaids. I have seen several gentlement wearing buckle brogue/shoes, as I do, and a few more wearing diced or argyll hose.

When I go to a black tie function it is really the only time I ever get to "dress
to the nines" and I enjoy doing so. I am fortunate to be able to afford buckle shoes and diced hose. I like the look of them with the kilt, so I wear them.

I don't like fly plaids, so I don't wear one and as it is not a common sight here, I do not feel the compunction to wear one. If someone wants to wear one to a black tie event however, I say let them do it.

There are very few white tie events that a "commoner" as I am, would get invited to in Australia and as such I look to the black tie event as the peak that I am likely to reach.