If you are focusing on the value part, it follows what John and CW said.
The reason items from the past become collectable is because very low low numbers (compared to today) were intentionally squirreled away for future sale, which is not what happens today. People are trained to think (by collectable industry, including some model train companies) things should be stored unused and then reap a huge profit someday. Problem is everyone is doing it, so there is no shortage when people try to "cash in".
Post War trains in general were played with. Hence why they are readily available in the secondary market, but a very nice condition item can be more scarce and carry a higher value. There was a (unfortunately deleted) thread around a week ago regarding a box of old Post War rocket launcher rockets (5 of the 6 that were in the master box, all in their baggies) that sold for over $2500. You will never see 5 standard PW rockets sell for $2500 if they are just loose parts, even if in good condition. This item was because it was not as common as if you just collected 5 rockets and sold them together.
There is a great example in the baseball card world. Anyone remotely into baseball cards knows of the 1952 Topps set, and the standard stars (Mickey Mantle, etc). There is a story of another player, named Andy Pafko that is actually one of the most valuable parts of the set.
Casual observers would say "who the heck is Andy Pafko?" (no disrespect meant to Mr Pafko or his career).
The thing here is, kids in the 50's also used baseball cards to put in the spokes of their bicycles to make noise with. Many sets are arranged in numerical order when assembled. Andy Pafko was the card numbered "1" in the set, so was often on top. As a result, the number of surviving Andy Pafko cards in good condition from the 1952 set took a huge hit. Link to Andy Pafko card info from PSA graders.
Nothing like that happens today. Ask all the people who were going to fund their retirement with Beanie Babies from the late 90's. A lot of people had similar ideas, so most are worthless.
If you are collecting because you like something, your set of 6464 boxcars is still collectable, and it's now a relatively easy thing to collect. Most of the modern 6464 series cars can now be had for little money (the ten 3 packs and also the single add-on pieces, of which I forget exactly how many there are).
You may pay a slight premium for the 1st set, but that's about it. Years ago, it was standard for the "6464 Series One" set to sell for $300 or maybe more, and people used to try to get $1000 for the 10 sets, (driven by the 1st set value mostly), but I believe those days are in the past.
-Dave