I think I get what you mean: Because it is the constitution, it must be abstract and serve as guiding principle.

However, I beg to differ. Here is the full latest constitution:

Chinese: http://www.12371.cn/special/zggcdzc/zggcdzcqw/

English: http://news.xinhuanet.com/english/download/Constitution_of_t...

As you can see, the paragraph on "beautiful" is just a tiny part of the constitution and the word "beautiful" only appears once throughout the entire constitution. So it is probably not something very "guiding" and "central".

Also, the constitution touches on a lot of aspects of the society, so I wouldn't be surprised if it is amended to include a small mention of the "look" of the physical landscape.

I would say that the word is added just to make sure that the party keep environmental concerns and "good outlook" in mind while working on all the other tasks.