Does anyone else buy two of almost everything? Engines, cars, tools, supplies, etc. (just one spouse)
Remember the late70's and 80's when Postwar Lionel prices were higher at every show? During that period two of my friends bought 2 of every car in the Lionel catalogs, thinking that they would keep one for themselves and sell the duplicates in 20-30 years and make a killing. One even called it his "retirement fund".
Boy were they wrong, about 2 years ago they sold everything to a dealer for .20 cents on the dollar.
My philosophy was, and still is, buy what you like and play with it. Play value, not monetary.
Now that I have absolutely no room for acquisitions, either on the display shelves (nothing gets stored away in boxes) or on the layout, I sell stuff to make room for something I want more. Tastes change. What I do is look around at my collection and say to myself: "Self, if I saw that car today, would I buy it?". If the answer is "No", up for sale it goes making room for my newest treasure.
If I sell it for less than what I paid (usually the case nowadays) so be it, I received its play value already and whatever money I do get for it goes right into my train bank for new (mostly Postwar) goodies