Several of the categories in your poll are true for me, so I picked the one that pushed me into it.: "receptive agents are as hard to [find] as receptive publishers". But self-publishing IS easy these days (and not just via Amazon - I use FeedARead in Britain, which is very inexpensive, produces a good-looking, print-on-demand book, and distributes to more sellers than just Amazon). And I do think that a stable of self-published work can impress that elusive agent or publisher. Let us not forget successes from self-published beginnings, by authors such as Andy Weir.
I prefer a combination of self-publishing and working with an independent publisher. I do all--or almost all--the work myself and then see if I can find a publisher. For two books I did--a women's anthology and a novel--this worked nicely. The publisher gets all the work without any investment, and I get a book I can feel very proud of.