I'd be curious to hear how some of you are tracking the ROI on your SEM efforts. With the dealers that I've worked with it's ranged from "Throw money at it and hope something sticks" to "measure VDP views, form submissions from SEM and hope that impacts sales" to "DMS matchbacks via email addresses and phone numbers"
So I think the answer to the question "Am I spending too much on SEM?" has to be based on quantitatively measuring the impact on the bottom line. Looking at clicks, impressions, CTRs, etc doesn't tell you much. They're useful metrics to track over time, but they shouldn't be how you measure ROI. Tracking phone calls, website conversions, VDP views, etc is better, but still doesn't tell you if you sold anything. Looking at finalized deals in the DMS and tying those back to phone calls or website leads that came from SEM is going to give a much better picture of the ROI.
And that is still imperfect. But if you are tracking all of those things then you can make a much more informed decision about where to allocate that digital spend.