It's been awhile for me as well.
You can buy a external drive from Apple and the songs purchased on the iPod can be reversed back onto the Mac.
The content that wasn't purchased on iTunes you likely will need to rip again from cd's or check on macrumors.com or in the itunes forum for the latest restoring tricks and restrictions.
If I recall there was some sort of upgrade process that replaced the rips with higher quality ones for a bulk price or something.
Won't I-Tunes Match take care of the stuff ripped from CDs, as in loading them then depositing into Dropbox or Airdrop then to the computer? I haven't tried jut remember reading it. Also if they are backed up with Time Machine and backed up to the cloud or an external drive, like someone else alluded too, you might be able to move them. I've been able to move stuff from computer to computer using home sharing but not from pod to Mac or PC. I'm not an expert just a user.