There is no question that the muscle car segment has softened-drastically...and will probabley continue to. I have placed (sold/brokered) over 300 vehicles since 1999...If it is an investment that motivates you, your safest bet is to stay with the 70 and 71 E-Bodies with the 426 or 440-6. While the target market has shrunk, there are still buyers for these authenic, numbers-matching, low production cars. Of course, one must be knowledgable, have balls of steel, well connected and have numerous cream cans of cash buried in the back 40 to successfully do this!
On the other hand, the softening market will create a great oppertunity in other areas. I have noticed a shift of interest to the A-Body segment in the last 6-9 months, followed by interest in driver-quality Chargers and Roadrunners. The winners (short-term) will buyers of upper-end, driver-quality vehicles.