Here are some things that worked for me (and I HATE that room!):If anyone can tell me if it's just a matter of attrition and I need to kill all the wraiths or if it is a trick of timing the jump to grab the crystal from the ceiling (like grabbing the candles in Seer Augustus' house early on), I would be very grateful.
1. Use a Crystal of Time...might help dodging the wraiths and timing your jump (backflips work best).
2. Summoning a Guardian Angel (or whatever they are called) can keep the wraiths busy.
3. The last time I played I let loose with a Blast Nova between the wraiths...and they were destroyed instantly and never came back. I haven't tried it again, so it may have been a fluke. Although it may be that if you can kill them in one shot, they won't regenerate.