[DaveBlake]

If I wanted to transfer the downloaded additional data to a new system I would use export to single file and then import that file.

You trust your computer more than I do mine.  One file, and the computer's in charge of sucking it back in?  I get the creeps when the computer has too much power.    I like having all the labelled folders, I can open them and see what's in there, I can read the nfo files.  

I trust the software I wrote to do the sucking
You can read the xml file too, uses the same xml tags as the NFO files. But if human intervention (even just checking) is something you want to do then I can see why you would want to use separate files.