The Wagner card, which measures a dinky 1.5 by 2.5 inches, is so valuable because of its rarity. An estimated 60 of the cards still exist, many of them in crappy condition. Wagner himself earned $10,000 annually for playing baseball in 1908, making him the highest paid player of his day. $10,000 was worth a lot more back then, obviously, but Wagner could hit, field and steal with unparalleled skill. Not bad for a bowlegged, barrel-chested kid from Pittsburgh.
In the 1903 World Series, Wagner's Pittsburgh Pirates lost to the Boston Americans; Wagner had an especially rough outing, batting just .222 for the Series, and this after he had won the NL batting title. A special "hall of fame" for hitters requested a portrait of him to honor his batting crown, and Wagner refused on the grounds that "I was too bum last year. I was a joke in that Boston-Pittsburgh series. What does it profit a man to hammer along and make a few hits when they are not needed only to fall down when it comes to a pinch. I would be ashamed to have my picture up now."
They don't make 'em like Honus Wagner anymore, do they?