Jeez, Dale, you are hereby renamed Chief Gringo Looter. The Inca War Princess should like that title.
You are of course right, a lot of the railroad heritage is disappearring, and any preservation is better than none. There are some sad situations like "La Argentina". And wouldn't it have been great is the SV had been able to get the mallets out of Guatemala.
But preservation is happening. I've visited and been impressed by the Guatemala museum and shops, you've ridden the Esquel line, and there are many others I have only heard about...Sao Joao del Rei, etc. They actually got a train running in El Salvador again, even if briefly. The GyQ limps on.
Part of the problem is the stuff that will be most attractive to buyers will also be the stuff most likely to be preserved or maybe even used locally.
But in the end economics hopefully will solve the problem....transportation is expensive.