Great link Steve, I will have to look into it more when I get a chance.
My advice is educate yourself before buying, and then collect what you like. If you are pulling things from circulation, then just pull out what you like. At worst it loses a little buying power if it isn't anything truly special, but it brought you some joy until you spend it. Then, at best if you pull something out that you and others like you can make a profit above face on it when it is time to part with it.
For example I photograph star notes before spending and then keep in my wallet until I have to use it. I can't afford to keep anything above a $5 but I can always have the picture to remember it and know it is in my wallet until I use it.