Hi Michael, I have been working with PHP-Nuke for over 2 years, installing for friends and even for personal use. I have been using PHP-Nuke since v6.5, so I have carried out the upgrade procedure numberous times, and also have an excellent insight into the system. The upgrade procedure is as simple as replacing the core php files (keeping language files intact), and as for keeping everything the same, when updating the database, only the field properties are updated, the actual values stay intact!
Looking forward to hearing from you,
Xcentric (Designs).