I hate these 'rules'. Cultural appropriation had a specific definition in a specific context. It now has become virtually meaningless, because cooking spaghetti as a Brit would be cultural appropriation by this new (and insane) definition.
Clothes are clothes. Let people wear what they want. It's obvious when it's disrespectful. I'm from an area that has a very distinctive national dress. It's often worn as a costume over here in the UK. No one cares, because no one feels worried about offending Germans. I don't care much either. It's very easy for me to see when it's worn as a piss-take and is an easy signal for me to avoid those people. I've also seen hen parties or similar have a good old time dressing up in the dresses and I say, go for it.
I know there's an argument about profiting from cultures (when companies cheaply produce stuff that has value in a certain culture, etc.), but I honestly think that's a problem caused by capitalism. If you wanted to wear my traditional dress bought from a traditional dressmaker or company, it would easily set you back hundreds of pounds. Get a horrible knock-off made of polyester from China and it's #20.
Ultimately, all of this leads to more division. I have various traditional outfits from countries I have no familial ties to, that were given to me by people I worked with in those countries. I couldn't wear them now here, because I'd get attacked for it by a bunch of 'right-on' friends I have. It's so beyond stupid. We should be happy to share our cultures.