Here is the thing about infix: the lack of infix probably does hurt, but not lack of the arithmetic infix. There is various syntactic sugar used in programming languages that is front-and-centre, expressing program and data structure, used everywhere.

I believe that most programmers won't have that much problem with (+ (* x x) (* y y)), but even those who don't will balk at cruft like (aref a 3), and (slot-value obj 'foo).

In the TXR Lisp language, I provide a set of well-targeted syntactic sugars for things like this; sugars which do not disturb the surrounding Lisp expressions and don't introduce ambiguities (precedence and associativity).