@ Richard
"I am no longer relying on third-party lead providers, i.e. Dealix, Automotive.com, etc. Is this really a good idea, or should I still be buying those third-party leads? "
Richard, I think this is a great idea if it's working for you. I would also say with the way 3rd party leads have been looking lately, I doubt you"re missing much. Anyone else getting a flood of really bad leads over the last few months?
Getting back to the question; you have to decide what your marketing mix is going to be and what's going to give your dealer the best ROI. Just because all the other dealers are buying 3rd party leads does not mean that you need to be as well.
"I’m looking to take this one step further and add some display advertising"
My dealer/s do a lot of display advertising, including site re-targeting and we do most of this with JumpStart automotive. Overall we have been very satisfied with JumpStart.
You really have to dial in on your market to know if display advertising is going to make sense. Like PPC, you really want to be sure you're tracking everything and be sure that your message continues all the way through the click pattern.
@alex "Can anyone give their insight on doing SEM with a provider that creates landing pages vs a provider that sends traffic directly to your website."
Great question - I think this should be a separate posting all together. Initially I have seen both work and both fail. Most landing pages ask for the marriage before the date while the homepage can let you date the customer but too often the date is not a good one and the customer turns you down.