Do you want to memorize the exact words or just the general ideas?
(Side note: for more discussions on verbatim text memorization see how to memorize a book.)
For text like this I wouldn’t use a specific memory technique, but would memorize the two parts separately and then have one split the other:
"Simplicity--the art of maximizing the amount of work not done--is essential."
can be broken into:
"Simplicity is essential."
and
"the art of maximizing the amount of work not done"
For me, it would be easier to think about the sentence like that before trying to remember it. Manipulating the grammar in my head would make it memorable.
If you have trouble recalling it without mnemonics, try picking a few keywords and creating mnemonic images for them. “The art of maximizing…” makes me think of “the art of memory” and max functions, which would lead me down a chain of obscure associations related to programming. Or “Max Headroom” – a TV show I never saw, but that everyone was talking about when I was a kid.