Hi Jim,
Josh from Mail Shark here. With regards to your question, both carrier route mailings, where you mail to everyone in a specific area and specific targeted vehicle mailings work.
I think the question comes down to what you are looking to accomplish. Are you looking to increase car count in general or are you looking to just bring in specific makes and models?
If you are looking to increase car count in general than my recommendation is to do a carrier route mailing. As you mentioned above the cost is significantly less than a targeted vehicle list mailing. The reason being, is the cost of postage and the cost of the targeted vehicle lists are much higher than the standard carrier route mailings & lists. Therefore, you are able to target more prospects with the same budget.
However, if you just want to only bring in specific makes/models than the targeted vehicle list mailing is the appropriate route. That said, a large portion of the success of this type of campaign has to do with the quality of your list. Specific car information is not available through the DMV. This information comes from multiple self-reported sources and all list providers data is not created equal.
I highly suggest reading this short blog post below that explains exactly what you need to know and gives what to Ask Before Buying a Targeted Vehicle Mailing List.
https://www.themailshark.com/resources/blog/where-targeted-auto-lists-come-from/
With regards to what works best, that also depends who you ask. What I can tell you is that direct mail is highly effective when done properly. What does done properly mean? Here are a few of the variables that will have an impact on your direct mail response rates.
1. You strategically choose the best mailing area (Below is an article that explains how)
https://www.themailshark.com/resources/blog/defining-your-auto-repair-shops-target-market/
2. You remove addresses that may be less than desirable from your list.
3. You consider removing your current customers from your mailing if in fact you are looking to do a new customer acquisition mailer.
4. You have the right creative with the right messaging and offers. This is something that many miss the mark on and is arguably one of the most important keys to the success of your marketing
5. You have the right strategy of targeting prospects more than one (Below is an article that explains the concept of frequency and reach)
https://www.themailshark.com/resources/blog/frequency-vs-reach-which-is-better-for-my-direct-mail-campaign/
6. You understand how to track your response rate not only thought call tracking but most importantly through the use of a match back report that compares new customers to the mailing list. Many customers don’t call directly from the mailer. Many will go online read reviews and call from your website or the number shown on google, etc.
7. You understand and have a realistic expectation regarding ROI. Below you will find a link to a Direct Mail ROI article as well as Case Study showing the results from an auto repair shop
https://www.themailshark.com/resources/calculators/auto-roi-calculator/
There is much more involved than what is stated above, but hopefully gives you a bit more transparency to some of the important topics that need consideration.
If you have any questions or would like to discuss some of these topics, I am always available.