I don't think you understand what FLAC is. FLAC is a lossless compression format, that's it. FLAC also can be encoded in 16/24 or other bitrates like 24/192. Moreover, you can't (or shouldn't) do lossy to lossy encoding, so if you want to future proof your collection, you should store it FLAC or another lossless format because when/if mp3's go obsolete, you'll be stuck with it.