As I just started multibox I still in pain from all the expenses from CD Key, Burning Crusade and Game Cards, hehe and soon 3x WOTLK.
It really doesn't worh taking N copies of CE. Or do that: Buy 5 CE and 4 Normal. Use the CE and 4 Normals. Save the 4 CEs and sell later on eBay for 100% more. :P