Paint, Materials and Different Variant Models
That got me thinking about more twists and turns which could influence sales in an interesting way, and hopefully not represent a ridiculous amount of work.
Paint:
I remember one of the devs dismissing paint as anything important and I thought about it and disagree. I think paint should reflect an eras tastes and furthermore that new colors should be the fruit of research because in 1940, all cars came out black because we didn't have the technical means to have economies of scope and pump out cars of different colors as customers wanted. So cars could come out as red, white and black, or maybe a larger variety all according to player choice. On one hand you might take up more of the market, and on the other you might waste money producing cars in colors no one wants.
Secondly, this is slightly more part of my tacky era-copying desires, having custom stripe decals to denote the high-end model. (examples: Golf GTI, 205 GTI, Mustang GT350 ect.)
Materials:
I am not talking about carbon fiber here, but rather about bumpers and door handles. The switch from chrome to plastic around the 70's-80's probably meant changing the machines required to make them and maybe research to make sure the bumpers have the proper strength and safety rating.
This research or buying of machines could mean you would be able to change between chrome and plastic (and chrome-looking plastic? like on new cars), and reflect the era's tastes better by having two identical models of the car, one with a black bumper, and another a chrome bumper, but also door handles, those circles around lights and indicators as well as grills and vents.