The primary value, to me of Lisp syntax is that code is represented as data structure literals which can be manipulated as easily as any other data structure prior to execution. Clojure has that; it just comes with literals for a few more data structures and uses two of them, vectors and maps in the syntax of built-in forms.

Why would arguments in Lisp (= "list processor") form a vector?

Is it so that the syntax of vectors can be used? Then it has technical consequences.

Is it because of technical issues (arguments are vectors internally) and thus it can be exposed in the syntax, too?

Or both?

I think the motivation for making the sequence of arguments in function/macro definitions vectors instead of lists was primarily syntactic - to make them look different from the body. They're definitely vectors internally though.

How do square brackets break the syntax? Aren't they just syntactic sugar for (vector ...), exactly the same as ' is syntactic sugar for (quote ...)?

And imports, obviously, are just special forms. It's not like Lisp doesn't have others. It's still an S-expression, so why is it problematic?