Some random thoughts...

About caps: It's interesting that the founder of The Scottish Fiddlers Of Los Angeles, Colin Gordon, the only actual Scot in the group, invariably wore a deerstalker with kilts. Makes sense: we have a lot of sun, and the deerstalker keeps the sun both off the face and off the back of the neck, the places you really can get sunburned here. (By the way, it's strange perhaps that Los Angeles was home both to the first Strathspey & Reel Society outside of Scotland itself, and also home to the largest branch of the Royal Scottish Country Dance Society on earth. The huge LA branch has since split up into two or three smaller branches.)

About baseball caps: Back in the 70's it always struck me, on visits back to the South, how all men and boys seemed to wear them. Almost nobody wore them in California at that time. Now they're very common here.
What's more, baseball caps have become standard Pipe Band dress. Not only American pipe bands, but pipe bands in Scotland and everywhere else have baseball caps made up with the band's name and/or logo on them, which band members wear whenever they're not actually performing.

About Highland Dress in the USA: Indeed here can be seen, at any US Highland Games, the wackiest possible mixing of various time periods and modes of Highland Dress on a single person. It can involve such things as 18th century shirts and great kilts worn with Prince Charlies and modern bonnets and any other anachronisms you can imagine. Add some Native American moccassins, modern sunglasses and mobile phones, and you've got the picture.
One guy had ghillies with no socks, a bit of bare leg, and then some military diced hosetops, a great kilt, antique long horsehair military sporran, Victorian dirk, Jacobite shirt, targe and claymore, topped off with a crudely knit bonnet with long feather. One sees this sort of thing at every Games.