Deleting Content\* will also delete your profiles and savegames...
Deleting Content\00000...\* would delete your DLC, XBLA, GOD, NXE Installs and TU's stored there... (basically, everything not specifically for a profile)
Nothing on your HDD is "Important" in that you can restore whatever is there by using a XEXMenu CD, Dashlaunch configuration loading stuff from a USB Memory or so...