I think it would be not that much better than prefix.

Infix is easier to read, because it is just more natural to parse. An expression like:

sin(1 + (5 + x + y) / (n + k)) is just really easy to understand

(sin (+ 1 (/ (+ 5 x y) (+ n k))) is inscrutable, at least to me.

The second thing is, intermediate variables makes code much more readable, but lisp strongly discourages this. The only way to create a lexical variable is with LET. But this causes indenting, which is pretty ugly. In fact, the use of indenting for both logical nesting and variable creation is a really nasty thing:

so this:

    def qualifies_for_free_shipping(item_price, weight, shipping_factor, category):
        if category is in FREE_SHIPPING_CATEGORIES:
            return True

        item_cost = item_price * TAX_RATE
        shipping_cost = weight * shipping_factor + 2.00
        total_price = item_cost + shipping_cost

        if item_cost >= 80:
            return True

        if total_price >= 100 and category in ELECTRONICS_CATEGORIES:
            return True

        return False

becomes, in some lisp dialect I am making up but is like common lisp

    (defun qualifies-for-free-shipping (item-price weight shipping_factor category)
      (if (in category FREE_SHIPPING_CATEGORIES)
        t
        (let* ((item-cost (* item-price TAX-RATE))
               (shipping-cost (+ (* weight shipping-factor) 2))
               (total-price (+ item-cost shipping-cost))
          (if (>= item-cost 80)
            t
            (if (and (>= total-price 100) (in category ELECTRONICS-CATEGORIES))
              t
              nil)))))

I could have cleaned up the code and used a better conditional than nested if's or something, but this is my point. I can't just glance at the code and see what is going on, I have to parse it and keep track of where I am as I move around the s expressions. In the python version I can just jump in the middle and move around without keeping a mental bookmark, because I always know from indentation how I can get to where I am now.