Value of a clean modded '72 Duster?

I think 12-15K with everything done if you find the right buyer. Modded classic cars are harder to sell then stock. I think if its a really clean car 10K would be about right. Unfortunately you will get to a point were upgrades arent going to add value as much. At least thats my opinion.

Heres a clean 72 that sold advertised at $19,500. Original 340 car slightly modded. Im sure he got less then his asking price.
http://www.cars-on-line.com/49585.html


Heres a clean but stock 71, 318 car for $4500
http://www.cars-on-line.com/59276.html

Prices are all over the place now.