I wonder if iTunes match might help.
an Ars Technica article wrote:
Another question our readers asked was what happens if your library is filled with higher quality rips, such as tracks encoded in Apple Lossless (ALAC) format. Matched tracks will still be in 256Kbps iTunes Plus format, while uploaded tracks will retain their original format. Tracks aren't replaced in either your iTunes library or on your devices unless you request them to be, so the lossless files in your main iTunes library will be safe. Sticklers might balk that matched tracks won't be available via iCloud in a higher-quality format, but if you don't require lossless quality on your mobile device, having access to smaller 256kbps AAC files via iCloud may be a benefit.
I'll be curious to see if they offer something like a find and replace all option, specifically for people who ripped their CD collections at lower bitrates.