Bloomsday, Trekkies, and Grown Women in Wizard Robes: A Common Thread?

An interesting question on fandoms and how they arise:

Bloomsday is fannish behaviour. It’s the same sort of thing as a Star Trek convention. Most authors don’t attract a fandom. There are exceptions: Conan Doyle and Jane Austen come to mind. But Ulysses? True, it’s a limited fandom — I don’t think anyone’s ever written Ulysses fanfic — but it’s a genuine fandom, and I’d like to know what there is about Joyce or Ulysses that permits it.
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Re-enactment isn’t necessary for fandom. I don’t think it’s something prompted by detail either. Conan Doyle tells us very little about Sherlock Holmes (and even less about Dr. Watson) but there is a distinct Holmes fandom. On the other hand, you could probably conduct a whale hunt using Moby-Dick as a guide, but I know of no society, “The Shipmates of the Pequod.”

I've never been a big Joyce fan (too attached to plot, and I find wordplay for its own sake wearying). Why does Ulysses capture the imagination so? This is sort of a Henry Jenkins question, but it's been a while since I immersed myself in that particular scholarly pool.