Some writers only want to raise one child at a time. That's fine. But, being a throwback in so many ways to a different age, I prefer to start a big family right away and see them all grow up together.
And as I said in those comments, since these are not works I have deadlines for, why not write them at my own pace, and on my own schedule, until such time as one of them gets big enough to demand all of my attention for whatever time it takes to finish it? There are already plenty of things I have to do on a specific schedule and to meet specific deadlines.
So, Matt, to run this metaphor totally into the ground, none of my novels are abortive (to use your initial metaphor in a way I'll bet you never intended). All of my children are planned and wanted and carried to term, and hopefully given birth. Some will be raised by me to someday become full stories. Others might die of sickness along the way. While others will be given away to be adopted by others (Oh dear God, when will this horrible extended metaphor end?) who can give them a better home.
As far as the notion Chris raised of waiting for the right mix of ideas to come along to make a so-so idea come alive and suddenly flourish -- that works too. In fact I'd have to agree that it's an essential part of the story-building process. And it happens so often that two ideas that don't on first examination seem to go together, often end up combining in ways wherein each perfectly brings out the full woof and thunder of the other.