I was talking with an economist friend of mine about the 99-trims problem, and we came up with a couple thoughts that might be helpful. The main one was this: after calculating attractiveness to each market demographic, instead of calculating sales in batches by demographic, generate large numbers (i.e. millions) of unique customers and calculate their car purchase decisions individually. An easy way to do that would be to represent each customer as a randomized mixture of market demographics - e.g. 77% Luxury, 15% Offroader, 8% Commuter - and calculate the desirability of each car from the weighted average of their demographic preferences and a (very small) random styling preference term. So, for example, a car that had a rating of 80 for the Luxury demo, 25 for the Offroader demo, and 45 for the Commuter demo would be a net 68.95 for this customer, and probably lose to a car with 75 Luxury, 50 Offroader, and 50 Commuter (which nets 69.25). A computer that can run the engine calculations can run these calculations as well.
In essence, this would reward making 99 trims … but only somewhat, and only if each trim has its own advantages over their competition. Which is pretty realistic, actually. Especially given that you already plan to include a brand Prestige rating which would penalize the troll brand for making so many crappy cars, and because every new car you make adds extra fixed costs for distribution, marketing, etc.
Another major suggestion my friend had was to incorporate a world population map into the game and dealer distribution strategy. Economists apparently know techniques for calculating the value of convenience to customers - these could be used to make having dealers closer than your competitors give you opportunities to steal sales from them.
Also, better cars can sell for a higher price. In fact, holding supply constant, they will sell for a higher price. This will probably be another balancing mechanic helping balance sales of cars of different qualities, while rewarding manufacturers of superior vehicles.