Discrepancy in hard drive space; can I delete these files?

You can certainly delete the two temporary items in your list:

• /System/Library/Caches/com.apple.coresymbolicationd/data/
• /private/var/folders/zz/CFNetworkDownload_L4uNTH.tmp

Avoid deleting the folder structures but large files in these locations can be safely removed.

To be extra safe, restart your Mac first and then remove any files. The restart will ensure the files are not in use.

Getting rid of these files is a great move, but keep in mind many of these caches will regenerate. For instance, spotlight files will regenerate at a cost of high processor usage and noisy fans (in a MacBook) immediately (look out for mds in Activity Monitor). MobileBackups is backup data from your iPhone which you might want on hand if you lose your phone and which will probably replicate the next time you plug it in.

Don't forget that if you sleep your computer, you'll often end up with a sleep image the same size as your physical drive. As we are almost all using flash drives now, don't forget flash drives need about 20% free disk space for self-cleaning and maintenance (I'm thinking of the SSD's which do their own garbage collection like Samsung and most of the Intel SSD). Spinning disks can go down to 10% but anything saved after about 50% usage is 1/3 or more slower than peak performance.

Clean out the files but think about upgrading the disk or moving some files or applications off to external storage. Time to go and follow my own useful advice. We humans generally procrastinate on important but not urgent tasks.