Is the /Developer directory still needed for Xcode in OS X Mavericks?
You can delete this folder. The new /Developer is located in /Applications/Xcode.app/Contents/Developer, so /Developer can be deleted.
As of Xcode 4.3, the /Developer directory is no longer needed.
See: https://developer.apple.com/library/ios/documentation/DeveloperTools/Conceptual/WhatsNewXcode/Articles/xcode_4_3.html#//apple_ref/doc/uid/1006-SW1