2015-12-10 -- My concerns are no longer valid.
- It's easy enough to FTP-download the images, and re-upload them to a new place.
- Exporting and importing the "WordPress eXtended RSS" (WXR) file is trivial.
- A simple XML file is small enough that there should be no file size concerns.
While there are export and import features in /wp-admin/export.php, I did some thinking and research to learn that there some issues with the functionality.
- Importing a large database is non-trivial
- There is no file/image backup-and-restore
Changing URLs requires setting changes or database editing