No different then any other hobby. Look at petroleum, oil and gas. How many signs and pumps do you need ? How many rolls of silver dollars does a coin collector need ? Answer: as many as make you happy, that is what a hobby is all about. And wouldn't we all love people to part with all the hard to find parts. Well in most cases that collection took them years and more money, road time and research then you can imagine. You buy it when you see it, cause you mite need it or trade or cash for something you do need or just enjoy it. There's no rules, just envy. So if you really want something you can't just buy, get out there and search for it. It'll be rewarding when you find it, just like the guys that did that to build their collections, and you'll find the thrill of having a hobby you enjoy. If not, try scrap booking for a hobby.