Anthony, the importer is intended for vBulletin 3.8, but it may well work with 3.7 and even 3.6. To be honest, we haven't sought out older installations to test.
Regarding moving server, it's more convenient to move server with attachments in the database as they can be dumped to a single file along with the rest of the data, but restoring them from a database dump can be more of a pain than just copying the files. I would move them in whatever medium they are currently stored and not worry about making a change for the sake of a server migration.
I'm sure importers will come, but why develop importers before the stable version is released?
Like it was posted elsewhere, many of us have vB licenses and might be willing to convert to vB3.8 first.
I've done it for one, offered to another who never got back to me.
I find MyBB the best Free Software actually...the only thing that is wrong with it is that there is no real development, but the features are comparable to the Top Paid Software. Not to mention I find MyBB the easiest to design(xF is coming close)
I'm pretty sure as soon as XF goes gold, we will see mods released in droves soon after. Many developers are waiting to make sure last minute code changes/fixes don't break there mode to keep problems, support and development minimal. There's been a surprising amount of mods released prior to a stable XF. Wait until XF is released as a stable version. WOW!