In my research I have found that most cars don't diminish in value drastically (bottom out) until they are about 7-8 years old. Once they are this old it becomes difficult(or impossible) to obtain a loan using the car as collateral. No standard loans mean that the majority of buyers have to have personal lines of credit or cash. The car could be immaculate with low miles but if the average joe doesn't have the means it will most likely drop in value. As for the value of it in 20 or more years only time and government regulations will tell.
I say drive the wheels off of it and bury me in it.