lot of talk about the inadequacy of 16/44.1 compressed tracks recently. The thing that makes a big difference is the bit rate of the compressed files and one of the side-effects of the iCloud music storage system is that it matches your low bit rate tracks and lets you "upgrade" them to 256kbps.
Good instructions on how to go about the upgrade are here. Basically you sign up to iCloud match (just do it in iTunes), submit your collection, then delete all the matched tracks with a bit rate under 256kbps. Finally you re-download them.
I was pleasantly surprised by the number of matches I got. The vast majority of my music is ripped from CDs I own but there are a few others in there that were happily matched.
The new collection will be quite a lot larger than before but with the price of disks these days I don't see it as an issue.
Apple's recent announcement about "Mastered for iTunes" and the future prospect of upgrading to uncompressed tracks shows the way forward.
All this is more reason why we need faster broadband now and in the future when we want to listen to our collection streamed live from the cloud.
Over night my library finished re-downloading all the matched tracks. My iTunes folder was 85GB before, now it's 98GB.