Don't know Murph, don't know his background--I do know 12 years as a local gives you insight into an area even knowledgeable tourists often lack. Possible he doesn't know about the "secret" parking lot--the vast majority of guests don't. And that's not a slam, there's no real signage for it--I first learned about it through word of mouth. But as someone who still goes to DTD at least twice a week, I can tell you it's NEVER close to even half-full.
Interesting theory on the cars, but you would think the effect would be more pronounced at, say, MK. Driving past that lot 2 to 4 times a week this Summer, I can't say that's been the case. Even Fourth of July I don't think they had opened the farthest-most Villian lot. Wouldn't we be hearing about MK and DHS closing thier lots due to capacity more?
(For the record, I know fewer guests are using ME. However, most WDW lots were built for a different, pre-ME era, and are therefore so big that any bump in cars won't be all that noticeable. I think the boom in restaurants along West 192, as just one example, is far more telling.)