It really depends on what you're looking to get out of it and what you've invested in the truck/future truck.
If you've invested 30k in a complete restoration (I don't know why people do that...), then you'll have to find someone to give you that and more. Harder to do these days when they can probably find one thats pretty darn nice for 15-20k.
These trucks ARE becoming more popular... but that doesn't necessarily mean more valuable. They clearly wouldn't bring as much money as say a 69 Charger for example. (in my opinion)
