The "Million Dollar Challenge" is a publicity stunt, intended to be used as a hammer by skeptics against the paranormal. It is not in any way scientific, other than perhaps being scientifically designed to ensure that it can never be won.
Randi deserves credit for coming up with a good publicity stunt, so you have to give him that, but lots of other people caught on quickly and so designed similar stunts: Challenges to prove evolution, the age of the earth or that Jesus is not God ... all equally unscientific and designed to never be won, only used as a hammer.
It has been pointed out that the rules of the million dollar challenge (specifically the required levels of proof) could be used to throw-out any number or cherished scientific beliefs, from the big bang theory to abiogenesis, because it doesn't meet scientific requirements for evidence ...nor is it designed to do so.
http://www.dailygrail.com/features/the-myth-of-james-randis-million-dollar-challenge