If your husband or boyfriend likes it, Then go for it. Personally, I enjoy wearing skimpy clothing in winter because it makes my Hubby horny. A lot of times he requests I wear something more revealing, Even if it's really cold. I don't believe in saying "no" to my Man, So of course I do it. It's not super comfy, But it brings me joy knowing it makes Him hard hehe. . .
As for appropriate - I'm not that radical of a traditionalist to tell women what's appropriate to wear. Different Men like different kinds of girls, So dress according to what kind of Men you'd like to attract. Or, If you already have a Man, Dress according to His tastes and desires.
Clothing is just clothing. Ideas about how a person should dress, What's "proper", "formal", "appropriate", Etc. . . Are made up by humans and if history is any guide people 1000 years from now will think we dressed very silly and have their own ideas for how people should dress.
If you want to bare your midriff in the winter or even just go shirtless, Go ahead. To me that looks uncomfortable. Maybe if I learned to use meditation to control my body temperature then wearing less clothing in winter could be a good exercise.
There is no reason to turn in the crop tops just because the summer is over. All the girl has to do is to complement the crop top with cropped sweater or cropped hoodie and also if it's really cold open jacket or coat. This way she can enjoy her favourite look all (or almost) year round with minimum discomfort. In the case when temperature is very low or she is forced to stay outside for a long time it's always possible to close her jacket or coat as needed to warm the belly up.