There's been several topics on reading Civil 3D Property Sets on the FME forum, and according to the release notes for FME 2019.1 support seems to have been silently added:
-------------------------- FME 2019.1 b19527 20190309 --------------------------
Civil 3D: Added read support for property sets [FMEENGINE-10155]
-------------------------- FME 2019.1 b19540 20190327 --------------------------
Civil3D: Read property sets from CAD entities as well as Civil entities [FMEENGINE-10155]
However I'm having trouble in getting it to work in a reliable manner and there doesn't seem to be any documentation of the extent of the support.
Is this a bug? A limitation in the current implementation of the Property Set reader? Or am I missing something in my current configuration?