I remember when I first started learning German, I thought it was useless. But after getting used to it, when I switched back to English, I was like where are all the nouns? Why is everything lowercase? It's all about what you get used to, I guess.
To maximize information content (entropy), we must try to use all symbols with equal likelihood - which this rule assists, employing capital symbols with closer to equal likelihood than their usual rarity.
Furthermore, said symbols must convey previously unknown information - which this rule does not, as the nouns have the same meaning whether capitalized as not, and the "information" conveyed is redundant.
Human languages aren’t usually concerned with maximal information density though. Multiple layers of redundancy are often present. Features like noun verb agreement, grammatical gender, pleonasms, and even redundant words (last will and testament, vim and vigor etc) are used in various languages despite the redundancy, to increase clarity.
In English, nouns are often spoken with stresses in a sentence, which could make capitalizing them a pronunciation issue, just as other punctuation is (e.g. commas for pauses, question mark for changing intonation). I don't know about German, though.