Well technically, you can delete the entire contents of the sd card without harming the phone. Apps that keep data on the sd card will re-create those folders as needed. Only you know what you want to keep and what you don't want anymore. You'll need to browse through all the folders to view the contents and decide from there. You have too many folders for someone like me to describe the contents of each one, and most are obvious anyway.
First thing to do though is to make a folder on your PC named something like Droid Backup, and copy the entire contents of the sd card to the PC, so you have a full backup of everything before deleting.