when it came to quality , you have to remember the "D" arent newly manufactured, all of them are converted so if the original SKS are of good quality then "D" it converts to will be of reasonable good quality.
good quality or bad , back then most people werent gonna pay alot for a SKS that accepted an AK mag so the price sold was only $25 (or 25%) more than standard SKS but look at the price spread now and that is simply bcos nobody imported any lately.
so yes, the smart money back then was to buy a "D".
BTW: a "D" peaked in 2007 at $600 , while a standard SKS was $169.