Your understanding of Japanese culture as “minimalism” is very shallow. Have you ever seen the “sumo banzuke” (sumo ranking)? It makes the Yahoo Japan website look empty. You see, “Japanese culture is minimalism” is no different from saying “French culture is impressionism” or “Spanish culture is cubism”. Minimalism is only a part of Japanese culture and is neither dominating nor central theme. It’s something that non-Japanese takes notice of because unlike other cultural elements, it’s something that they don’t have in their culture.
Also, you should stop assuming “this is how Japan/Japanese should be” and look without a prejudice. A good example is the photo of Shinjuku that you used. Notice that while left and right sides are lit, there is nothing lit up or down. A Japanese person with a clear destination in mind will ignore all neon except for his destination or the most noticeable one nearby. With this in mind, check Yahoo Japan website. Notice that the central section is blue texts with yellow markers while left and right sections are colorful and have icons. Yes, this website is arranged in the similar way. If there is nothing interesting shown or if you have a clear objective, you use an icon on left or right (and some in the central section) to rapidly move to the desired contents…while those using Yahoo website will be scrolling down trying to find something interesting or what they want while staring at photo that they don’t care about. (BTW, this Yahoo website reminds me of newspapers that you have to keep flipping pages to get to the news that you want.)
Finally, about “kawaii”. If you listened closely, you would have noticed that girls would be speaking it with different tone, pitch and intonation to indicate how much they agree with each other. They would only continue to discuss the same topic (dog, in this case) if they feel there is a sufficient amount of agreement to continue it. This audio cue is unapparent to non-Japanese because they are too busy trying to understand words or expect the disagreement to require different words (such as “no” or “can we talk about something else”).