As others have said, they were expensive back in the day. When my parents were first married (c1952), my mom found out my dad never had trains and thought that was a shame. Her brother was buying trains for her nephew (who was all of 9 months old!) for Christmas of that year, so she decided that her gift to my dad was going to be trains, told her brother that whatever he bought, double it. Her comment was there weren't discounters back then, but there was a place in Brooklyn at the time that would give discounts if you bought a lot. I still have some of those trains, the 671 engine, freight cars, dump car and other pieces. She said it was a couple of weeks salary for her (as an office manager), but worth it.
Back then a kid would get a train set, if lucky, then would get pieces on birthdays and such. Even when I was growing up, mostly in the MPC era, new trains were expensive (on the other hand, you could often, for 30,40 or 50 bucks, get a huge lot of trains someone was getting rid of, my father got something like that in the late 60's, included several engines, accessories, 027 track and switches, kw transformer, bunch of stuff) for like 35 bucks. ).
One of the problems with all of us is we have gotten used to an economy where things become cheaper. In the 1950's tv's were ridiculously expensive and obviously were crude and primitive. In the 1955 tv sets ranged from 130 bucks to 1300 bucks in 1955 dollars (easily 1000 bucks for the low end one in todays dollars). A thousand bucks today will get you an oled tv with a 60" screen, 4k display, etc etc). Appliances were expensive, too (though they likely lasted forever, one plus on them), you name it. Cars today dollar wise are expensive, but if you look at the cost but then look at how long they last and the relative lack of maintenance required, they are a lot cheaper than cars back then. Your smart phone has more computing power in it than the entire computing power NASA had in 1969, for 500 bucks (and can do a lot more). The problem is trains didn't follow this trend, in large part because they are not a mass consumer item. If they sold as many trains as let's say Samsung does tvs, that 1500 buck engine would probably be 500 (and if there was real competition, prob less).
Lionel is interesting, in the golden age of the 1950's I wonder what their margins were like vs how many trains they really sold. My guess is their margins were high and that their sales, while obviously more than today, were not as large as you might think (in terms of units), it sounds like Lionel, while they had low end stuff, was kind of aiming at the high margin/relatively low volume business even back then (and again, this is relative. Were Lionel trains popular back then? Yes. Did they sell as many of them as video games today? I really doubt it). While a lot of kids might have had trains, because of the pricing model, few would have a lot. Not to mention the other factor, how many of these were bought by parents with their eye on them, too?
As far as the value of post war trains goes, yes their simplicity made them easy to repair (same with older appliances), and because of that and the sheer number available between originals and reproductions, and the parts out there, so they can keep going. As far as their value as collectors items, I am dubious about that. I doubt modern engines and such will become collectors items, with some exceptions, but I think the post war/pre war won't be a big deal either. As with pre war, post war trains will likely be valued for being a rarity, a 700e will probably be a collectors item, the post war versions of it won't likely, because it was an original. Over time what will happen is the common postwar stuff, the runners and even stuff that has been collected, won't be worth much, whereas specific, rare items might fetch a lot, like the "remote control' sets or the ones that allowed using two engines on the same track.
My take? The prices what they are. You can get discounts today, and also there is a used market, so there are always way to be able to get trains on a reasonable budget.
