I think you're right about the degree of difficulty in identifying most of these from photos. In the case of fungi, lack of detail (often just a "cap shot") must make it difficult for the knowledgeable. But we do have some good mycologically-focussed contributors (though Fenwickfield is sadly missed).
The user-unfriendly interface may not help, though: nor the fact that (as I have found), if you pose a question in a comment ("what sort of habitat?"), the person posting often doesn't reply. Maybe (s)he has lost interest, or is too shy to admit not noting enough at the time.
I enjoy seeing posts of organisms outside my ken: marine posts, f'rinstance (having been landlocked most of my life): DJM and others produce fascinating photos. And I find that some more recherche posts lead to to spend even more time I than I can really spare following links from them.
But it's not just the rarer types where we could do with more input. Hymenoptera are one case in point: a couple of good people here, but lots of species to know about.
People can, of course, also post on the specialist web sites - although a hymenoptera-based Fastbuck page I tried made it clear that they weren't an identification service, more one for observations of behaviour etc. But the Hoverflies group there, DIptera info, and some others are much more helpful. The point is, we want those critters posted HERE!