I think you summed it up clearly, Jeff, when you deconstructed the issues with the 3rd party leads.
Let's face it, the quality of many of the 3rd party lead providers are subpar or suspect at best. However, they're only suspect because of the circle jerk of lead selling (and re-selling) to the multiple different buyers of said leads, from OEM to additional 3rd parties. (It's a profitable process, so you understand the financial gains from doing it).
I have no problem with 3rd party leads and would gladly recommend them to my clients IF they are all originating from the sources in which the form field existed. Some online shoppers may prefer submitting their information through these sites rather than individual dealer sites as it puts out a bigger net, and they feel they are being looked after by the organization. However, I believe the quality gets watered down the way leads are transferred and multiplied through their lifecycle. Give me a lead organic to the original site, where the call-to-action is realistic, and is exclusively sold/directed to only one dealership, and that is a very valuable lead.