Mike, I think something else that is important to look at is where the pro-Union Southern troops were raised. The more inhospitable the ground (forests, hills, swamp) the less likely slaves were present and the more likely pro-Union troops were to be raised, e.g. AL, TN, TX, etc. The only state that did not field independent pro-Union troops was South Carolina, which had the highest concentration of slaves (and was also the first state to leave the Union because of slavery).
El Tejon,
You know where West Virginia came from, don't you?
It seceeded from Virginia, and was admitted to the Union in 1863 as an independent, anti-slavery, pro-Union state.
You're absolutely correct that regional economics had much to do with whether the residents were pro-South vs. pro-North.
I think it would be a really interesting exercise to look at the individual delegates to the state secession conventions and the state legislators, their votes on the issue at hand, and the underpinnings of their personal economics.
I'd not be surprised at all to find that those whose livlihoods had few linkages to the slave economy would be more likely to want to maintain ties to the Union, while those whose personal economies were tied tightly to slavery would be more likely to vote for secession.
It's also very, very interesting to read through the history of the souther states during the Civil War and see how they, in fighting the north, experienced many of the same problems that the colonies experienced when fighting Great Britain 85 years before, where individual colonies often put their own interests ahead of the collective interests of the United States. Several times early in the war those competing interests almost sank the bid for independence from Britain, and it was a continuing problem throughout most of the war.