Most of it is probably worthless. I have no idea why people spend thousands of dollars on some of stuff.
The only thing Ive really spent time on is the NBA one. To me its like collecting cards, except for I dont have to worry about their rating. Im not sure if they will ever have value, but if you limit yourself to the $10-$20 packs you probably arent going to lose much either. From the last $19 pack there were a few that sold within the week for $10,000+. The most expensive was Lebron #23 (the moment is of his first game winner ever), it went for $40,000.