Number one, stop taking things I say.
Number two, you're exactly right when you say "in your heart" its worth way more than $500. In my heart, my car is worth exactly what I paid for it. In my dad's heart, his is worth at least $15,000. Reality, though, dictates otherwise.
You state your car has numerous missing parts, ill-fitting parts, and some random mechanical issues - all of which doesn't bother you because you own it, know it, and accept it, just as I don't care that my car has been in two accidents and my father's was nearly totalled. But put yourself in the place of someone like you looking for that car. Again, how much would YOU pay for it?
I can't blame anyone for not offering much for our cars because I wouldn't either if I hear the word 'accident.' The difference is - again - I know what happened, I was there when they fixed them, and I accept it. Same as how you accept your car's flaws.
Now, as for the truck. You live in a rural area, right? No crap the truck sells as long as it sort of runs. Heck, even here shitbox pickups sell quicker than better-condition cars...and often for more. People who buy older half-gimp trucks like that typically do it for parts, rebuild it, or run it even more 'till it dies doing things they wouldn't use their other, better truck for.
Its very different for a late-model car like yours. Its not super easy to mod - not as much as a truck or even a Civic - and there's not that much desire to do it anyway. People looking at your car want to buy it and not have many problems with it. Otherwise, they'll spend a few hundred bucks (no more than a grand) on a half-ass car that'll work for awhile before they can get a better car.
I would sincerely suggest you fix those problems or try to part it out.