Note that good-looking doesn't necessarily translate into well-usable. The examples of alignment and icon weight are more on the side of aesthetics. If there's too much consistency, e.g. everything aligned in the same color with same weight and similar icons, it gets hard to quickly orient on the page and find things. This seems to be a common oversight, even by large companies.
Visual "breaks", such as color changes, spaces, or variation in contrast can help a lot (and still look good). A good example are paragraphs in text: A large chunk of text is more difficult to go through, or re-discover some section, than one divided into paragraphs.
This is true. Also, over time, well-usable but not exactly the best looking can become the "standard" for good-looking after a while because the design becomes so ubiquitous. You could easily make a beautiful or good looking suite of airplane controls (call it a "rebrand"), but most pilots would probably call it disgusting because it violates the common standards and aesthetics that they rely on.
Visual "breaks", such as color changes, spaces, or variation in contrast can help a lot (and still look good). A good example are paragraphs in text: A large chunk of text is more difficult to go through, or re-discover some section, than one divided into paragraphs.