The only real "theming" that can be done to Touchwiz is to change up the colors of the launcher, maybe change the look of the launcher dock/icons and go in and color/change up the toggles on the pull down notification. Most people turn to 3rd party launchers if they want to change the look of the launcher, the notification pull down toggles is normally a standard "change" when it comes to any theme.
At least that is my take on it and what I always did when I was still creating themes back some time ago.