Interesting video.
I used to be big into cards, though not anymore. Thing is with rookie cards is that they're so expensive at first and if that player ends up flopping that card is worthless after. Kind of like buying stocks I suppose. I remember even when Eric Hinske's rookie card was big money back in 2002/2003. A couple of years later, could have bought one for a couple of bucks. Even Hideki Matsui's card was big money before he even played a game in the MLB. He went onto have a solid career, though I'm sure when Kaz Matsui came up his card was big money at first and then after a year or two was worthless.
Plus the value of a card is in the eye of the beholder. Usually to resell cards, you won't get actual book value unless you sell it to a fan of that player etc.