Colin, good post, with insightful comments.
As a straight pool devotee, I favor 8-ball because of the similarities of dealing with patterns, clusters, trouble balls, key balls and so on. I also prefer it because it requires a lot more thinking and planning than 9-ball. In 9-ball, unless something is tied up, the only planning is staying on the correct side of the next ball, thinking in patterns of 3. Conceptually, it's a very simple game, where execution is the biggest challenge. When a position mistake is made in 9-ball, it's usually pretty easy to duck and play safe; you only have to protect one ball. Not so in 8-ball. As Colin said, once you begin a runout in 8-ball, you have a much harder time playing safe when you run into trouble.
I do think 8-ball is easier to runout for one reason: Usually there are multiple shot opportunities, so it's generally easier to get control of the cueball on your first shot. Once a good player gets control of the cueball, his chances for running out the rack in any game go up dramatically. In 9-ball, often you come to the table and there is no shot, or it's a difficult shot that makes position play difficult. But once a good player gets a handle on the cueball in 9-ball, I think it's considerably easier to run out a 9-ball rack than an 8-ball rack, simply because there is less that can go wrong.