So true! I am torn between the "look over here, not over there!" approach and the almost too obvious "she went out for a jog and someone abducted her" approach. There's also the "If I hide the body well enough, they can't arrest me for murder" approach. I don't know which one he was going for.
My money is on option no. 2 because I think we need to look at intention with this case in particular, since it is IMO premeditated and not a cover-up. FD is also an extreme narcissist and most likely prone to overconfidence, which is a classic trait of the condition. JD stated that FD would make elaborate revenge plans on his enemies. Just a gut feeling, but I believe that he thinks he is the Pink Panther and that everyone else is Inspector Clouseau (minus the solving part). Therefore, I can see him trying to set-up a scenario where it would look like something else happened, and because it would be so well executed (due to his perceived cleverness), people would buy it at face value.
His best plan would not result in him being the prime suspect. Because, even if LE can't find the body, it is a very risky, expensive and drawn-out process, as well as very stressful and humiliating for him to be targeted. It also precludes or greatly delays him getting custody of his kids and collecting life insurance/trust funds/etc. The only thing that leaving the car at the park does for FD, if he's not trying to set-up a scenario, is create a diversion. I don't think he expected the initial attack to be so messy, so I'm not convinced he felt he needed to buy time just in case. Also, despite the messiness he managed to get rid of the body same day, as per his plan. If he feels confident she won't be found (I think he does), why would he care about delaying LE?
Case in point: this is a guy whose company is sitting on over a half-dozen multi-million dollar properties while he is going broke. His forte is not contingency planning or adapting to reality, IMO. I honestly believe he thought his plan would go off without a hitch, and did not expect it to go badly. The only thing that seems to have worked out for him, so far, is the disposal of the body. However, for a pre-meditated murder, that seems like the most straightforward part.
To sum it up, my opinion is that the car was a scenario and not a diversion. However, that does not mean the body is in the park, especially if he intended to make it look like an abduction and wanted to ensure that she would never be found, which is my guess. I think she is as likely to be in the park than anywhere else, based on our information. LE might have much better information in this regard. One can only hope that he underestimated LE's capabilities with hiding JD's body, the way he did with the license plates.