Improving on what Detroit did

Pricing should be set by the game like in Aerobiz (for the SNES and GEN) where you just adjust how far off the game's recommend price, same with wages and advertising. This removes boring fictional accounting work from gameplay. So many of the 90's business simulators go bogged down with entering numbers, it is just so much better to just move a slider, as it is hard to gauge how much you have to change the number to get the desired results when simply plugging in numbers.
Contracts, while your bread and butter should be general sale it would be nice if you were offered to bid in contracts for example the US Army looking for a staff car and later a 4x4 or a police department looking for a new police cruiser, they will have specific demands of what they are looking for and you'd issue one of your models to be considered, if accepted you have to meet their orders or face late fees and get a bad reputation yet on the plus side guaranteed sales.
Vehicle Reviews, have scores for acceleration, handling, breaking, ect with a final percentage and ranking to competing models of that type. Detroit kind had this when you tested vehicles but the review section was just a few words like good fuel economy, safe, affordable and never gave you a good idea of what you were up against.
Contracts, while your bread and butter should be general sale it would be nice if you were offered to bid in contracts for example the US Army looking for a staff car and later a 4x4 or a police department looking for a new police cruiser, they will have specific demands of what they are looking for and you'd issue one of your models to be considered, if accepted you have to meet their orders or face late fees and get a bad reputation yet on the plus side guaranteed sales.
Vehicle Reviews, have scores for acceleration, handling, breaking, ect with a final percentage and ranking to competing models of that type. Detroit kind had this when you tested vehicles but the review section was just a few words like good fuel economy, safe, affordable and never gave you a good idea of what you were up against.