Well, yes. The Wikipedia article I linked does indeed say that this is a hypothesis, which means it hasn’t been conclusively proven yet. But it does also list a number of reasons that lead to this hypothesis being proposed, and there’s a long-ish paragraph on the research that has been done on it. But yes, as long as it’s a hypothesis, it’s still in the realm of speculation.
It seems however that your experience does somewhat back that up, judging by the “if you can find a buyer”. Basically, what I’m saying is, that if depends on or determines whether an artwork falls into the uncanny valley. If you can find one, it was on the other side of it. If you can’t, then it was in it.
Basically, picture the graph from that article, but instead of “human likeness”, we label the x-axis “artistic appeal”, and the y-axis “amount sold for”. Get rid of the dotted line, and on the solid line we replace “stuffed animal” with “broad appeal” and “corpse” with “niche appeal that doesn’t sell”, and the far end of it we label “niche appeal that DOES sell” and place it much higher up, to where “healthy person” is. Hope that makes sense.