interesting...
Never used WavPack but there's a comparison at the bottom of this page (
http://flac.sourceforge.net/comparison.html) between FLAC and WavPack.
Between those two it look's like WavPack can do better compression at the cost of CPU usage and time. So... based on that, I'd guess it's a matter of your priorities. WavPack if you're worried about hard drive space, but FLAC if you're worried about direct playback on a underpowered device (or device support).
But the ability to get your loseless file back from a lossy compression seems like a fantastic feature!
More discussion between WavPack vs FLAC here...
http://www.hydrogenaudio.org/forums/lofiversion/index.php/t43906-50.html