Can I pull a specific system property in an API call?

You cannot pull properties from the device endpoint, but you can filter -- the method is limited (supports only one property match). You can use a filter like so (if you wish to restrict to specific values of that property).

filter=systemProperties.name:system.groups,systemProperties.value:VALUE

We’ve generally ended up with a full dump of /device/devices/$device->{id}/properties into a hash and then we reference that data as needed with a simple wrapper function to lookup property values from the hash.  It requires more API calls, but actually is useful and it works. I checked all our code and we pretty much never use that first method.