If the Chevy Volt follows the typical depreciation model for Chevy vehicles after 8 years, I'd guess 25-50% of the origional cost. If you use the Chevy Malibu as an example, it's close to 33% of the original cost. So, the Volt should be around $13,500 - depending upon condition, miles, ect.
The Volt Battery has a warrany for 8 years, after that the estimated cost is $8,000 to replace the battery. Now, if you had purchased a dependable Toyotoa Camry, after 8 yrs the car value would still be high - but let's say that you have an 8 yr old Volt and an 8 yr old Camry - and you put $8,000 into each. With the Volt, you get a new battery (assuming the batteries will be available, and the price for a replacment has not gone up, substancially). It is my belief that the $8,000 replacement battery is optimistic, due to the market's rejection of this product. Replacement batteries will be rare, and the law of supply vs demand will dictate that if a replacement battery can be had - it should be MORE than $8,000.
However, the Toyota Camry can be nicely updated with $8,000 put into it. Rebuilt engine/transmission, updated interior, stereo, new tires and fresh paint - with some left over for more upgrades. Meanwhile, the same old worn, dull and dusty Volt will have a shiny new battery.
Speaking of the second-hand market, consider that many of the used Volts will come from Federal fleets. We know those cars will be shagged-out by the time they are declared surplus. Imagine buying a former Federal fleet Volt.
Excellent comparison. Love your screen name BTW. Winter is coming.