I'll lead you through my thought process as to why I've decided against it.
The first step to writing a story is to brainstorm ideas for one. I went to a fairly simple VN idea generator and came up with a bunch, only some of which I remotely thought were interesting. In the end I thought that none of them were really appealing enough for me to make a VN out of (I was looking for something that could be completed within one month) and wanted to go with a few ideas I had come up with in previous months.
So I went onto the next step, outlining the plot and characters. Still, it felt really forced, since the story had to be condensed so much for NaNoReNo. I managed to find some decent stock music, and maybe I could learn to draw sprites with a tablet... but for backgrounds, I was completely stuck, unless I wanted to limit myself to photo filters again.
But none of that is really what changed my mind. Instead, it was a much bigger question -- quality vs. quantity. Even if I decided to make a short VN, I could make lots and lots of them to make up for the length... right?
That isn't how it works. Making a story for the sake of making a story is just doing it wrong. You either have a good idea and a desire to flesh it out, or nothing. And if I can't come up with something that I truly find worth making, then I shouldn't consider working on it. It wouldn't be memorable, it would be done poorly, and it would be taking away time I could be using for a significantly better project.
Think about it in terms of other authors. After an author's Magnum Opus finishes, what are they going to do? Will anything else be as fun to read as that? No, of course not! They've set their own standards too high! The readers have become attached to the characters and setting of that one story, so no matter how good newer stories may be, what the reader truly wants is to continue following the old one. This might be the reason behind the success of those manga/anime which go on forever. Fans become fans of things for a reason, so isn't it only natural that a fanbase will lose interest in an author once they stop writing the things that hooked the fans in the first place?
So in other words, I'm sticking with Detective Butler. It's a solid idea with characters and plot, which is something a lot harder to come up with than I realized. And, while the amount of feedback I've gotten on it is considerably lower than I would have liked, it has also been considerably positive, which I didn't expect. I'll make sure it's as polished as it can get before releasing the final version, and see where it takes me next.