Definitely do NOT cache this value. The whole point is that we can toggle Read-Only Mode on by only changing config. I just went through a process of removing caching from our config infrastructure for this very reason. This shouldn't be slow (we'll be perf testing it) and if it is slow, there are some mitigation we could do.

Anything in CSCFG is designed to be changed in-flight (i.e. without even having to shut down the app domain) so caching it would be bad.