fwiw, you could convert those wav files to flac without losing any quality and save considerably on file size. you'd also end up with the added benefit of being able to properly tag them
It increases my storage, having two copies like that. But I think of the .mp3 files as my "mix tapes" that I wouldn't be upset to lose since I can make another at any time. :)
Backups are a requirement, now that I've gotten rid of the physical media. Local storage is on a mirrored drive array. I also have a copy on a Truecrypt'd drive at work, and another copy at a relative's house several states away. Online backup really isn't an affordable option for 350+ gb. :/