1. More than just a few fansNow, I myself consider 1 and 5 to be the prime tests of artistic merit, and while the jury is out on most of Cowen's preferred art as well as mine by standard 5, Manilow easily has the better argument on count 1. Criteria 2 through 4, on the other hand, arouse enormous suspicion in me, because intellectual fashions have been known to cause sudden upsurges in enthusiasm--extremely thoughtful, well-articulated enthusiasm, mind you, from the most authoritative quarters--for bodies of work that subsequently sink into well-deserved obscurity and near-universal contempt.
2. Self-critical fans
3. Artistically well-educated, sophisticated fans
4. Fans who give an account of the art's importance and depth
5. Test of time
My favorite example is Woody Allen, whose "serious" films were not so long ago--only a single pseudo-stepdaughter/wife ago, if I'm not mistaken--widely hailed as masterpieces of emotional and intellectual subtlety. Today, I doubt there's a self-important aesthete on the planet who even bothers to watch his stuff any more (apart, that is, from his early comedies, which really were masterpieces).
There are, of course, works of art that have been hailed as masterpieces by the cognoscenti for a century or more, despite evoking either indifference or outright revulsion from the vast majority of the public. (Think of late James Joyce, for instance, or early atonalist music.) I tend to think of those bodies of work as similar to the "cult classics" that manage to establish a small but often fanatically devoted and quite durable following. (H.P. Lovecraft comes to mind, or perhaps Ayn Rand.) They certainly deserve credit for something, but I'm not sure artistic genius is the right attribution.
In any event, the art Cowen describes hasn't even survived long enough to establish itself at that level. I therefore hope I will be forgiven for ignoring the scholars' breathless writeups and waiting at least another couple of intellectual cycles before concluding that minimalist and conceptual art is anything more than its worst critics (including myself) make of it.