[SuperNinKenDo]

Supposedly the QianZiJing was also widely memorised. The SanZiJing is a MUCH later text (probably half a millenium, give or take). That said, the SanZiJing is a much more pedagogical and all-round meaningful text. More value can be derived memorising it, as it is essentially a pre-Syllabus for a classical education, not only laying out basic principles, a set of texts for the student to learn, but also featuring an array of keywords that a curious student with access to a good teacher or extensive library can follow up on, all contained in an easy to memorise summary. QianZiJing by comparison is a fun and interesting literary curiosity.

[SuperNinKenDo]

I would, however, add that traditional Chinese character learning involved the complete memorisation of a text, followed by learning the characters associated with each word of that text. Learning individual characters in the way we think of as "traditional" today is actually a modern innovation compared to how people used to do it. In that context, memorising a text that consists of 1000 purely unique characters takes on a different character, even though I would think people would be better served just memorising more useful texts.