I think one has to tread lightly when attempting to mix clothing of two very different -- and very recognizable -- styles. One runs the risk of making the outfit look like a costume, and worse than that, a very mismatched costume.

In my opinion, two things are very important to consider -- restraint and context. By restraint, I mean that if one wants to give a "nod" to another culture or style when wearing Highland Dress, one should keep elements of that style to a minimum. In other words, it would be better to have a Highland outfit with a bit of Western flare than a hybrid half-Scottish/half-Western costume.

The other thing to consider is context. If I were at a Highland Games in Texas, I don't think it would look out of place at all to see a man in a kilt and a cowboy hat, or even cowboy boots. That same outfit in Michigan, or in Braemar, would look really out of place, and even run the risk of looking silly.

If you live in the American southwest and a western-style shirt is part of your typical wardrobe, then wearing a western shirt with your kilt probably wouldn't raise any eyebrows. On the other hand, if I were to wear a western-shirt with my kilt here in NC, it would look a bit odd, because people in my area don't normally wear western-shirts unless they are "dressing up" like a cowboy. So if I were to wear such a shirt with my kilt, I'd be wearing two unusual items of clothing which together don't really have anything to do with one another. I think the look would be incongruous and confusing to a lot of people. But, as I said, if I lived in an are where that style shirt was in the norm, it would be a completely different story.