My suggestion (and I'm new to vB, but not upgrading/moving forums):
Set up two test-beds. One you will do a clean install of vB 3.7 and import the database, the other you'll just upgrade and fix whatever needs to be fixed (or, hopefully just overwrite your mods with newer versions

).
Whichever is easier and works more properly, that's the winner

Just my opinion. It's what I did when switching from SMF 1.1.4 to vB 3.7.