Implicit in this whole thread is the idea that the only value in an old model is as a collectible piece. This point of view arises from two sources. First, some doorstop modelers tend to act more like collectors than like model railroaders. That is, they tend to value models based more on age and rarity then on accuracy to prototype or whether it fits their modeling interests. This is not a knock by me -- as is often said here, there is space in the hobby for everybody -- but it does engender a certain amount of scorn from a lot of people in the hobby. The second reason that doorstops are often perceived as valuable only as collectibles is the belief of many modelers that accuracy to prototype and level of detail are the only measures of the value of a model. Note in passing that this can lead to collecting of a different sort -- buying a model just to admire the detail, with no regard of whether it matches the modeler's actual railroading interest (assuming they have one). I don't subscribe to either point of view, and will claim that there are other reasons to have an interest in old models.
Like many model railroaders, prototype matters to me, especially at the railroad, region, and era level. That is, I like assembling and operating complete trains that are a reasonable representation of the real thing -- freight locomotives should have a matching caboose and a historically appropriate string of cars, etc. As an overlay to this, I value the efforts of the individual modeler more than the amount of detail on a model. That is, I find hand-built kits and scratchbuilt models to be far more interesting as exhibits of the art of railroad modeling than models made by either machine or paid skilled workers with no interest in railroading. Not surprisingly, I have wound up with a roster of older models, as that is where most of the modeler-built cars are. I do, however, have an accuracy threshold -- it has to look like the real thing in basic proportions, or I am not interested. And I don't fancy fantasy models.
On a side note, I understand Carey's doorstop cutoff at the mid-50s, but I think the Penn-Erie models that came later also qualify as doorstops. If an all cast metal GE U50 is not a doorstop, then what is?
Speaking of which, does anybody have one of the Penn-Erie 65-ton GE switchers? Looks like a 44-tonner but was a later model. I have never seen one except in the LWS newsletters.

- Penn-Erie GE 65-ton Switcher.jpg (206.6 KiB) Viewed 5669 times
Jim