Reprint money for short stories is gravy. The writer does no additional work, but someone gives you money anyway. The question is: How much money? What is the second (or third or eighth) printing of a story worth? Especially since the story can often be found on-line in a pirated edition for free? (I have been having more trouble with pirates.)
I have no consistent policy. For very small foreign magazines requesting the rights to translate and print my story for free (i.e. Latvia), I usually say yes on the grounds that (1) I will pick up new readers in Latvia, (2) the magazine is making no money or next to no money anyway, (3) the market is very small, and (4) I think it will be cool to be in Latvian.
Other foreign markets offer small but consistent reprint fees (i.e. ESLI, in Russian), and those, too, do not trouble me. American anthologies usually pay an amount consistent with what the original publisher offers of they decide to put together a bunch of stories from its various issues. The sticky question for me is textbooks.
I recently (yesterday) signed a contract for a very, very low payment to reprint "My Mother, Dancing" in a textbook aimed at college-level English and science courses. I won't say how low because it's embarrassing. But this editor, a professor at a prestigious college, spent eight years convincing a textbook publisher to take on this project, which will be a massive collection. She wrote me, "In order to keep the textbook from costing $120, which students can't afford, I need to do it this way!" I believe her.
Especially since, more and more, I receive university requests to reprint stories for free in "packets" designed for a specific course and usually limited to a run of twenty or so. I say yes, because how much money could be made from twenty copies, and anyway I like the idea of my work being taught in college classrooms.
Does this all make economic sense, in that students will then be moved to buy my novels, according to the Cory Doctorow Doctrine? Or is it just one more way of eroding a writer's always shaky income? I have no idea.