The problem with reusing it is the parts you don't see. Yes, it might look shiny and new but there is more to the story than just how it looks.
The race car oil in your truck sounds like it was bad for your truck. The reason I say this is, maybe it looks pretty and new, but the story lies within the compounds. Time, pressure, and heat can easily change molecular structures.
The reason I say this is especially in a flat tappet engine or where oil can see high temps, or "load" the structure of the oil is changed as it's squeezed and heated protecting the engine. What this does is it literally sheers the molecular bonds and this breaks the oils down. When this happens it's load sheer factor is reduced and begins to allow wear depending up on how long it's used. Just because there is "oil" there, doesn't mean the oil has any beneficial properties left to protect the parts it's on. You can't "filter" away the bad oil from the good.
So, by all means use the oil as a drill/machining lube, or quenching parts, or lubing non-essentials or minor things. But, if it's important, use new oil.