One unintended consequence of VW buying back all the TDI cars is that prices of used TDIs will quickly rise above what VW is willing to pay. If VW offers to pay the value of the car before the scandal plus $5000, that "floor" creates an immediate arbitrage opportunity for people to buy a car at auction then flip it to VW. Auction prices will therefore quickly rise to a value just below the VW "floor" and will exceed it for more desirable cars.
I believe that auction prices are the only reliable source of information on used car pricing. NADA and KBB publish prices for private party sale and retail price at a used car dealer at various percentages above those auction prices, and they will do so for TDIs just like they do for every other make and model. If insurance companies publish their own data for use by claims adjusters, that data will also have to reflect the premiums nice cars receive over the price VW is willing to pay.
If you have an unfixed low mileage or well maintained vehicle with popular options, you can offer it in a private party sale for more than VW will pay you. Assuming the demand for fun to drive cars with good mileage doesn't die, people will pay those prices for desirable cars.
And for the next two years, if your car is totaled by a lusty buck during rut season, an insurance settlement at FMV will exceed what VW would be paying you.
Auction prices will be much lower for vehicles that receive an emissions 'fix" because those vehicles are no longer eligible for the VW buyback offer. The interesting question is whether VW will fix high mileage/poor conditions cars and then poison the market by sending them back for sale at auction. Doing so would be very bad for TDI prices. Much better would be taking such vehicles out of US/Canada markets by crushing or exporting them to other countries. If the cars are exported without a fix, they will need a new VIN to prevent them from being reimported.
From a game theory point of view, I think the best strategy is to wait for VW to establish their buyback prices. But don't give your car to VW right away.
If you want to get rid of your vehicle and feel it is is desirable, get VW's buyback price and then offer it for private party sale. Anybody who wants it will need to pay you a 10 to 20% premium over the buyback price--and nobody else will be underselling you for a TDI. They buyer is protected by that same floor in case they experience expensive repairs, their circumstances change or they get in a crash. You have two years to make a deal, which should be plenty of time.
If you want to keep your vehicle and are willing to get it fixed, game theory says to wait as long as possible. Let people in CARB states be the guinea pigs and uncover problems with performance or reliability. The $5000 compensation for the fix will still be waiting for you--or you might decide to sell the car before the two year window closes.
