There will always be exceptions to everything. For the most part, 99.9% of baseball cards from 1980 to present are worthless. There are Wall Street Journal articles on this. I've seen cases of sealed baseball cards sell for $10.00. The hardest part of giving free advice is that some owners have banked on having truly prize possessions. Yes, the rookie cards and the other .01% of the cards can be worth something.
Link on Baseball Cards from Motley Fool
Sure, if physical space is not a problem, keep everything you can. Everything has the potential to increase in value one day. Real life, people move and move on. Things are donated, trashed, or sold.