oss-security gets relatively little use?
You must know another oss-security. The one I'm subscribed to is very much alive and an important source of information for me.
It gets little use in the sense that only a small fraction of vulnerabilities are reported there, and there are very few non-advisory discussions (often by the same 2-3 people).
It does get use in the sense that every now and then, some vendor sends 50 emails that could've been one (most recently, some Apache Qpid thing). But I wouldn't call that part valuable.