Awards Ceremonies
Media events, particularly awards ceremonies such as Car of the Year can have a significant effect on popularity. Categories such as safest car, most economical, etc, etc, can make or break a vehicle. As a former car salesman I still remember walking into the dealership one morning to find my sales manager with his head in his hands because the company's new model had been savaged on Top Gear.
My suggestion is that, in addition to an annual awards ceremony with multiple categories, how about a event generator where your car endures a particularly good or bad review in a newspaper, car magazine, or TV programme, resulting in an appropriate impact on sales.