Wow, this is a big thread.
I did want to hop in and add two cents to some of Sean’s original comments.
Although I don’t have exact sales figures, I think it’s fair to say that novels have more selling power anthologies on average, but I also think that certain anthologies, Heat in particular, have more selling power than lots of novels. I think this has a lot to do with consistency. Heat comes out on a yearly schedule and people have come to expect good quality from it, so that keeps readers coming back for more. For many novels in the fandom, they are first-time novels or there has been a long gap since the previous one. There is nothing to “come back” to.
(To be frank, I know some buyers of Heat only buy it for the comics, but I’m not sure if this is a substantial amount to really alter the sales figures.)
As to the point of whether the current large number of anthologies help or hurt current writers, that’s a tougher question. I think they are selling reasonably well. Even though initial sales figures for Hot Dish (and Will of the Alpha iirc) were not great, they did pick up after a while, enough for Sofawolf (and Furplanet) to take a chance on more. And Rabbit Valley is doing another Trick or Treat anthology. People are certainly buying them.
But that dodges the question a little. Are anthologies, as opposed to novels, better for the writers themselves? I think this point has been raised in the thread, and I referenced it above too: anthologies help expose a writer to an audience. If we cut out all the anthologies currently going around and had everyone write novels instead, I’m not sure that they would sell well. Would readers take a chance on that many novels by people they have never heard of before? I don’t know.