Well I was hardly a serious stamp collector at 6 years old, and many of them were given to me by people we knew (neighbors, shop owners, relatives, etc) from letters/postcards they had received and saved. So honestly, I really didn't know much about any value or possible rarity, especially since most had been used and the postmarks showing the dates mailed (and from where) were kept intact. The doctor had brought volumes of books with him when he came over, and I remember him showing me the information about each stamp in my collection as he read the details to me. He also kept writing down the value for each one he really wanted/needed for his own collection which he added after examining them which totaled about $28 and a few cents. But then he said he would "take them all off my hands" if I would sell them for $35. For me it was a no-brainer as many of them didn't cost me anything, except for the more current ones Mom or Dad bought at the Post Office.
I do remember many in my collection were from countries all around the world as many of our friends and people we were acquainted with received letters from relatives, etc who lived or traveled there. And I can recall a little more specifically that some from the Orient were quite beautiful with bright coloring. Anyway, postage stamps were my very first collection and the doctor came to buy them when I lost interest. One of the VERY FEW instances in my life where I can say, "right place, right time"
Speaking of the space program, my sister collected (and still is stored at her house in Pacifica) just about every magazine, SF newspaper articles, and any other memorabilia she could find about the Mercury, Gemini, and Apollo (through Apollo XI) missions/astronauts, all kept in scrapbooks and binders. It's been YEARS since I've seen them, 1996 I believe. But I do agree that in general, collecting a specific type of item begins as an act of passion and monetary value isn't really considered, at least initially.