collect whatever interests them. Collections are so individual and should be. That's what makes it a fun hobby.
One of the things that a lot of people don't know is that many serious rock collectors special in one rock type or mineral group, just like baseball collectors that specialize in one area. There are also rich collectors that will pay millions of dollars for specimens. I knew a guy whose business was collecting, buying, and selling to wealthy collectors. He became wealthy himself.
Me? Like you, I just collect what catches my eye.