I was at a dealership ready to purchase an '11 sedan, then I popped the trunk and saw how much space there wasn't (including the diff bump). Ended up buying a hatch soon after.
I'd go with audio first. I really wish I could upgrade the head unit in my car for better sound and connectivity, but I paid for the nav package, so I don't want to just throw that away. Plus I just got a Q300 catback and I'm not impressed with the sound.