These items can be displayed throughout your house, they have different worths, and some are “special”. Each category has it’s own “rare” item that is quite expensive and hard to find.
You can sell any of these as soon as you find them, but for each there is a way to increase their value before you do that. It will still take a lot of time, but at least you’ll know what you are doing. I’ve set up a really thorough guide in my opinion, and it will lead you to the highest level collectibles. It may not seem like it at first, but honestly you could make a decent living off of gem collecting. Before I knew it I was wheelin’ and dealin’ thousands of dollars worth of merchandise and had a stash of ingots filling various rooms of my sims house.
First I want to say collecting is basically just for fun, at least at first.