I think mid-00s commercial OSes are a good target in this regard. OS X 10.2-10.9 and Windows XP-7 had a pretty good level of density while also feeling relatively clean and would be good to take some cues from.
I've been hoping Cosmic DE improves enough to be usable.
This goes against the original argument which is that icons should only be used for universal idioms that can be recognized by the icon _only_. Otherwise it's just noise