The sliding scale is a great idea.
Different people focus on certain features, for example, I think the the metal badge on the 1390131 is a big bonus, but the lack of LEDs on the 1390120 is a serious minus. Almost no one prefers the blue label to the beige (aka black aka white aka gray) label.
Most people are probably in agreement that the heavy plates in the earliest models are extremely desirable, and if it were me, and I found a heavy one in a terminal board, I would swap it with a standard 1391401 board and put $10 (at least) price swings (going both ways) on both boards to reflect it.
I would offer a "sound package" of substantial internal foam padding (I like the waffle drawer liner stuff laid flat and rolled into cylinders) and floss mod for $15-$20.
PS - I really lust over those rare super-early specimens with Model F style bar-code labels.