Ok, if you've got a lot of operators in one line, it can get difficult, but you're probably running into trouble reading it even without parenthesization. It seems like one of the huge wins of Lisp that you don't have to worry about this problem.
Like you say - why waste brain cycles trying to parse expressions. But then I also write comments in my code :-)
Were it not for the closed/licensed/expensive/commercial nature of Smalltalks, the language probably would not have fallen into to the relative obscurity it suffers today. I personally doubt that operators had anything to do with it. From what I've read of the history of the era, the language itself was much-loved and rising in popularity until the introduction of Java disrupted the traditional Smalltalk business models.
When conventional arithmetic doesn't "just work", languages will often give a first impression of being awkward, even though the rules of operator precedence are actually more complicated than just consistently using prefix or infix left-to-right.