9GB com.apple.coresymbolicationd file in Caches
No. Rebooting doesn't clear cache files in system. You would need to dig into exactly which subsystem creates here caches and determine of there is a way to manually flush them or move them to trash and then reboot to see when/how/what size they get recreated. 

I would boot to single user mode and use rm to clear that file since nothing is using it then. You could also use sudo mv /System/Library/Caches/com.apple.coresymbolicationd/data /tmp and then reboot. After the reboot you can delete the file from /tmp with sudo rm /tmp/data.

My hunch is you have Xcode installed and have introduced a large number of symbols into your database from one or more iOS versions so that Xcode can symbolicate crash dumps to assist in debugging apps using Xcode. However, it could also be a bug and whenever that subsystem starts recycling the cache, it will clear itself. If you can limit the number of SDK you use in Xcode, that might help as well. My feeling is the people with 60m files don't use Xcode, those with 1MB developer for one version of iOS at a time and those with larger size databases have multiple OS X and iOS SDK activated from within Xcode.