Speaking up here in defense of leggings...I said goodbye to my waistline a few years ago (because menopause) so I own five pairs of black 3/4 length Athleta leggings and wear them often (not in summer; I usually wear skirts or skorts then).
I have one pair of slim cropped jeans I like and feel comfortable in. Wide leg/barrel leg jeans look terrible on me. As someone else said, the silhouette is important and I am much more comfortable in an oversized top and skinny bottoms. I was in Edinburgh the last week of August and a typical outfit for me was black leggings, a sleeveless black linen tunic (to mid-thigh, like a short dress), a fitted jean jacket, Ecco sandals and a black cross body bag. I felt put together, comfortable, walked 10 or more miles every day, and didn't feel for one second that anyone was pointing and laughing at my leggings. My winter outfit is a variation of the above - tunic sweater or long sleeve shirt, scarf, coat, leggings, ankle boots or cute sneakers.
In any big city there are surely so many people from all over the world that you cannot say "no one wears____." Someone is wearing it. In Edinburgh there was everything from burqa, to Asian women in schoolgirl outfits with parasols, to puffy coats, to summer dresses with Birkenstocks. I was too busy enjoying myself to pay close attention to what the throngs of people were wearing.
All that said, I feel Paris might be its own beast in terms of the fashion vibe. No doubt there will still be tourists from all over the world wearing anything and everything, so I think you should wear whatever you enjoy wearing. For me, mid September is too late for white pants, and if I wore white pants in Paris, they would be filthy by the end of the day, so I wouldn't wear them. But if they make you feel great, or if your skinny jeans make you feel great, I say wear them.
