Well, according to the paint stats for high impact colors for 1970-72 (by percentage of production, 340 percentages are just for 340 cars)
1970 duster 340: plum crazy=3.2% , sublime=5.7% , go mango=5.7% , hemi orange=8.1% , lemon twist=11.3% , green go=1.7% , panther pink=1.9%
1970 duster: plum crazy=3.2% , sublime=2.2% , go mango=1.8% , hemi orange=1.4% , lemon twist=1.4% , green go=0.7% , panther pink=0.7%
1971 duster 340: plum crazy=3.6% , hemi orange=13.6% , lemon twist=1.8% , green go=6.5% , citron yella=6.7% , bahama yellow=5.0%
1971 duster: plum crazy=2.1% , hemi orange=4.6% , lemon twist=1.7% , green go=2.1% , citron yella=2.1% , bahama yellow=3.3%
1972 duster 340: hemi orange=11.7% , lemon twist=9.2%
1972 duster: hemi orange=3.6% , lemon twist=3.2%
Here's the rest of the high impact stats
High Impact Color Production % #'s
Of course, those were people's tastes back then, not necessarily now. For resale, I have to agree the highest value is usually the original color for the car if the car was anything special to begin with or if there's any originality to the car (numbers match, etc). I think that goes out the window if you've got a /6 car that's some '70's brown or green. Or if everything else has been modified. No point in the original color if nothing else is original. If there's no fender tag or build sheet, you can paint it whatever you want. And yeah, if you want to maximize resale you'll paint the engine compartment body color. There are quite a few mopar nuts that won't even
consider a car if the engine compartment is blacked out/not body color. Their take on it is that anyone that knows anything about Mopars knows the engine compartment should be body color, so, if it isn't it means that the person that worked on the car doesn't know what they're doing. So really it's not so much that the engine compartment is blacked out, it's that they figure the engine compartment color is probably the least of their worries because the last person to work on the car was an idiot.
Seems to me everyone paints these things Plum Crazy, Sublime, Hemi Orange or GoMango, because if you go to a car show that's what the majority of them are regardless of what they were originally. I personally think plum crazy is way overdone, and there is a reason car dealers refer to "resale red". If you want to do some "research" you could look at the aerial views from the Spring Fling meet, or any other of the big meets really. I just knew where to find the spring fling pictures...
The Giant Mopar Photo Gallery From Spring Fling!