Well, it's done. I beefed it up by nearly a third and sent it out to my agent. I hope it finds a home.
One thing which expanding Corsair has allowed me to do is to give the minor characters more spotlight time. One of them -- Anne Rogers -- got promoted from a secondary role to one of the three leads. She gets to serve as the moral center of the story, calling out both David and Elizabeth when they're being too amoral or ruthless.
We also get to see more of FBI Agent Yu, and the sinister Colonel Ghavami.
But the real treat was that I got to weave in an entirely new character. I realized that David needed a foil, so I created Halfdan. He has all of David's flaws cranked up past 11: he's even crazier, even more solipsistic, and even more amoral. I liked (or enjoyed loathing) Halfdan so much I made sure to have him survive in case I want to revisit these characters again.
I already have some ideas along those lines, and the real world has conveniently handed me Planetary Resources and their asteroid-mining scheme, so that it doesn't require nearly as much handwaving as I thought it might to justify space commerce and piracy less than a generation from now.
The next progress report on Corsair will be the pop of a cork if it sells, or sullen silence if it doesn't. We shall see.