I thought it was an amusing notion. Quite literally derivative by it's nature, but it won some accolades and I nodded my head. Good job.
And then, within a month, there were easily 50 copycats. PP&Z was SELLING folks. I don;' know the exact numbers but it was enough to catch the attention of several book publishers who said I NEED ONE LIKE THAT! And as the books wee literally over half written already, several industrially minded folks promptly sat down and pumped out imitations.thee were variations with vampires, werewolves and, of course, zombies. Many a writer, mostly writers I'd seen lament that the market was;t ready for their sort of work, sold books and crowed happily.
Know what? I haven't seen a lot else from those folks. To be fair, I haven't looked all that hard, but I remain suitably unimpressed by their writing skills and as I recall most of the reviews of their hastily slapped together classics + Monsters "fusions" were less than savory.
That said, PP&Z is being released as movie. Looks fun. I might even go see it. If it does well, it's always possible that some more "life" could be breathed into those ripoffs. Hollywood might need to see another one just like it. More power to all involved.
That is "Writing to the Market." It was only moderately successful because the books were over halfway written by the classic authors before they were "finished." Happily for them the books were already public domain so no lawsuits leaped out to wreak havoc.
It ain't for me. I write for myself. I always have. Happily, I seem to be in tune with the market now and then. Okay, rarely, but enough that I can eke out a living at this.
When should you write to the market? When hell freezes over. Beyond that it's not my thing. Your mileage may vary.
Mind you, I hardly have room to talk about being derivative. Me and a buddy cowrote BLOODSTAINED OZ in which the characters from Oz are dropped on Kansas via tornado. Only they're all vampires. But A) We did it first. and B) not a word of the original was used in the making of our gorefest.