This is an important topic, and reading Alex's account of what they go through brings into perspective the effort required to provide good information to potential customers.
Here's my 2 cents as someone both in search marketing, and who recently purchased a new car.
Often car shoppers do not want to pick up the phone or visit a dealership, they want to browse what is available at various dealers online and go from there. When I was shopping I had a few models in mind, but also had a number of options I deemed absolutely necessary in any vehicle I would purchase. I did find plenty of instances where I just didn't know if a particular vehicle included what I required.
May a dealer have missed out on a lead because of that? Absolutely.
So, what to do given the enormous amount of work that can go into vehicle listings...
An initial thought is to determine how much a lead is truly worth (how good are you at closing a deal?), how much time would be required to include all options on every vehicle, and how much would it cost to include all that data (fees, man-hours, etc.)? Does it add up? Is it worth it?
One way to reduce the amount of information to include on any given vehicle is to create pages which do include all that data, and track search traffic related to them. If after an appropriate amount of time you discover no search referrals for a particular feature/option then leave it out on the details page. Instead, focus on the ones that are bringing you visitors.
That information can also be had through keyword research, and you can even drill-down to your state for this, but nothing is better than data right from your analytics (there may not be enough data to register with Google at a local level:
Google Trends).
Also try using Google's search-based keyword tool. Input a URL for the manufacturer's options' page for a specific model, type in some options, and see what's given as a result (
http://www.google.com/sktool/#keywo..., sirius, moonroof, navigation, trailer brake)
You can also utilize data from your PPC program.
It will likely still be a lot of work to input the options people are looking for. So, I would certainly recommend including all available options for every model somewhere on your website (like a page for each model) to try and capture those customers who, like myself, need (err...want), and are willing to pay for, certain options. This can help capture them, but may not translate to a lead since the page is not an available vehicle.
Dan