It appears the new Google Music Manager for Mac can actually download all your purchased / free tracks an unlimited number of times, but it's not done automatically (you need to click "Download Purchased Tracks" and select a directory), and you can't tweak the directory/filename format, which is a bummer. If they added the ability to customize the template and let you choose a folder to auto-sync all new tracks to, it'd be the holy grail, and I'd gladly pay around double what I pay on AllTunes for the convenience and ubiquity.

Doesn't look like there's a corresponding update to Google Music Manager for Linux, though, at least not one that I could find (I was using my Linux machine to run Music Manager, but I'm okay switching to my Mac to get the download tracks facility.)