Fine art is, after all, an extension of religion. Just look at museums, concert halls, theaters, even arenas as temples.
That said, here goes:
Proprietors: Middle-class or desiring to move up, the kulcher-seekers. Subcategories those seeking familiarity with the old, beside those with “taste,” a little knowledge of “masters.”
Those dragged through: Spouses, dates, children.
Those seeking Experience: Usually modernists with “taste” but possibly those seeking play within art, qualities antithetical to where art must be “serious.”
Fellow practitioners: Usually too poor to collect new work except by trading, but also the most critical and appreciative, depending.
Now, for atheists and agnostics?
After drafting this, I see parallels to dining out for fine cuisine or attending concerts, live theater, even cinema.
Care to add to the list?