This is an interesting Topic, thank you Batman.
For my 50 years I had modelled the North Eastern Region of British Railways.
By chance in 2016, YouTube threw-up a (music) video of American Railroads.
I started buying American HO, used models from eBay UK and Hattons.
These were mostly Blue Box and I became very impulsive, buying models that I āliked the look ofā, almost slightly āaddictedā to it.
A good number of these used models were not 100% complete, it turned out - fingers burned.
I had learned enough to steer clear of 40ā Boxcars with peak roofs and roof-walks - but also, that I liked SW1500s, GP38-2s and SD40-2s.
Writing as a newcomer to USA Railroads from across the Great Divide of the N. Atlantic, but mostly through my being a Rookie on this subject, I have bought far too many models and not just B/Boxes.
I have steadily been disposing of surplus Locos and Stock via eBay, generally breaking even - but not always.
But I am pleased to write that I, like you can now resist the temptation - my two PRLX Executive SD70MACs are for me, the ultimate and I know it.
Age is another factor to also take into consideration. One day you, or someone else is going to have to dispose of your collection.
Having learned about and knowing now, how American Railroads operate and which models I would require to operate my layout how I want it to, I should have drawn-up a mandate of models required and then purchased brand new imports, from the major USA suppliers.
In the long term, this is a far more sensible and cheaper option.
Paul.