This has been noted before. I have seen a couple proposals to add significant whitespace to Scheme which I can't remember the details for offhand, and I believe was also the basis for the Pliant language's syntax.
One such proposal that I like is "sweet-expressions" at http://www.dwheeler.com/readable/. That page also has a rudimentary set of implementations for some Lisp dialects, including Scheme. It's too bad that new Lisp dialects never seem to take notice of these features.
Also, quick links for others looking for Pliant:
Pliant syntax docs: http://hc.fullpliant.org/doc/language/syntax
Pliant language docs: http://hc.fullpliant.org/doc/