Collect what you are passionate about. If you admire Jackie Robinson and want to collect his cards and memorabilia, do it and don't worry about the rest. If Ty Cobb leaves you cold, skip him. It's YOUR collection. if you are in this to make money, you are not a collector, you are an investor, and what you like/want is irrelevant.
Most important of all: we are all just a bunch of idiots pontificating on a chat board