(defface paren-face '((((class color) (background dark)) (:foreground "grey20")) (((class color) (background light)) (:foreground "grey80"))) "Face used to dim parentheses.")
(add-hook 'emacs-lisp-mode-hook (lambda () (font-lock-add-keywords nil '(("(\\|)" . 'paren-face)))))
Now they are fairly unobstrusive and stay modestly in the background, when you read Lisp code. IMHO this reflects their role in Lisp code: Lispers seldom look at the parentheses, they look at the indentation.