Peter,
It should be safe to delete the contents of this folder, it's used for the .NET Global Assembly Cache (GAC). I would leave the folder itself alone, just delete the contents. Worse thing that could happen is .NET breaks, and a reinstall of it should resolve that problem. (You don't actually need .NET unless you have applications that require its framework to run)
You may also use the gacutil.exe command that's included with the Microsoft Windows Software Development Kit (SDK), however it's a bit more technical.. It can be found here:
Gacutil.exe (Global Assembly Cache Tool)
A good start would be "gacutil /l", I personally would just stick with the above method.
I would also try running the dism cleanup command at an...