Short story: I suck at wordpress.
First, I backed up all of the html files via FTP, then backed up my SQL file using MySQL (via Hostmonster's cPanel). What I didn't do was export my blog directly from the wordpress dashboard.
Second, I removed files from the root level (removing the previous domain-level page) and then uploaded my wordpress install backup via FTP.
Third, I went into the settings of the /blog (old location) install and set both the WordPress address and site address to the new location (probably a mistake to change both, according to several articles I've read since then).
Fourth, nothing worked. I couldn't get back into the old install to fix anything (or export a clean archive from WordPress) nor did the new install work. I still have the clean database file but I accidentally replaced the original WP index.php with the post-armageddon version in my backup.
Now, I've attempted several times to create a clean install of WP using automated scripts in cPanel (easy as can be), and then delete the database files and bring in backup SQL database file. That seems to allow the old blog to load in the new (root-level) URL but when I attempt to access wp-admin functions I get errors saying that it can't connect to the database.
It seems like I should be able to restore the entire blog at the original location (I still have the database backup and a backup of all of the main content), but I'm missing something.
I've read around 40-50 wordpress-related articles and forum threads related to specific facets of this process and I'm generally confused about what my path forward should be. Most guides assume that an export direct from WP had been made, and I don't understand why my database replacement attempts aren't working. My guess is that it's related to the new domain, but I'm flummoxed.
Can anyone please help?