Great message Matt, and good grasp of the original post.
One of the things I'm noticing both in dealer sites, and discussion groups is the lack of service promotion. Sure, there are some who utilize it, but everyone has on their mind car sales, car sales, car sales. Outside of the site itself, social media is a great way to get in front of your customers EVERY day, with oil changes, check ups, tire rotation specials etc. Heck, if your dealership has a body shop, scratch, dent and touch up specials are another way. Keep your name in their mind, legitamitely, without spam, then you have them on the lot for a new car.
Oh, and guess who pioneered these social networking sites. Adult sites like Adult Friend Finder. Go figure. Start searching for sex, and end up with a lube job.