I felt a bit intimidated the first few times I went into higher end boutiques years ago, even though I was really mostly just looking, but I got over it. I don’t remember any unpleasant attitudes— at least no worse than the indifference of a young cashier at a Zara. ;-D
Now I’ll go in anywhere that strikes my fancy — in the states or elsewhere. I’ve made some great discoveries and even met some great people that way. Issey Miyake, Tibi, Stella McCartney, etc. I would have hesitated to walk in them years ago, but I now know better. They are just stores, open to the public, and no one is required to buy anything when they walk in a store, no matter the price point, demographic, or vibe!