I have both books, too. I always use the "Supercharged" version as my reference for the specifics of allowed foods on P1 and P2, since I know there have been changes.
"Supercharged" has a much more indepth discussion about our health in general, and I like the chapter about belly fat (which I have alot of.)
On the other hand, the original book has a chapter titled "Why Do People Occasionally Fail on This Diet?" which I think is a must read-especially now that I'm 6 months in and am experiencing slower weight loss.
So, hands up, for a serious "Beacher" I think both books are invaluable. I found the old version at a thrift store several months ago.