Having love the Rick James Anthology and browsing to see what I should buy next, I have found only two albums:

'Street Songs' (special editon) - which appears essential, and
his debut album.

But past this, I can find nothing that would further deepen my appreciation.

Surely, an influential funk great like James released more than a few albums?

He released several excellent albums but unfortunately,those albums are out of print.

'Bustin Out Of L7' and 'Throwin' Down' are must-haves.I highly recommend that you look for these albums.