I have been keeping the whole cardback, but that is because I'm too lazy to cut out the filecards. My 5 yr old thinks cut out filecards are cool. (Of course, operating a pair of scissors is pretty cool when you are 5.)

I don't know if eBay auctions give a slight edge to someone who sells a loose complete figure with a card vs a loose complete figure. (Although there could be the psychological thought that if a seller bothered to keep the card, he probably was pretty careful with the figure.)

I kept cardbacks in case I was ever to sell them, but come to think of that, it' really isn't likely....

CAse in point--> In an odd twist of fate, I have complete boxes (folded flat) for my ASP and Skyhawk, from the 80's. But those vehicles are so play-worn I could never sell them. Go figure...