To clarify, VALET PARKING (for which you pay $15 plus tip) and then walking to a theme park, hence leaving your car all day is COMPLETELY LEGAL. Parking in any resort's free car-park for more than 3 hours is COMPLETELY ILLEGAL. So, anyone on Dis Boards who jumps all over you for valet parking at the Contemporary and going to MK is a moron and doesn't know what they are talking about. I valet parked at the Contemporary 5 times on our past trip and left it there for many hours and was completely truthful with both the guard at the gate and the valet people and they were nothing but helpful, welcoming and friendly. They even started recognizing me by the end of my trip and calling us by name. So, once again, completely A-OK.
To answer a PP question about speed of receiving your car at the valet, I always found it to be very quick. The walk itself took me 7 minutes (but I walked fast, I had all 3 kids in the stroller, so I didn't need to walk at a child's pace) and then I usually waited less than 5 minutes for the car to be returned to me. Typically I handed in my ticket and paid and then while I waited for my car I removed my bags from the bottom of the stroller and folded it. Usually the car was waiting for me before I could complete the emptying/folding process. This is BY FAR the quickest method of getting into and out of the MK. Parking at the TTC and then taking either a monorail or boat to MK takes a long time and if you have a stroller, folding it and putting it on the tram thing from the parking lot to the monorail/boat is a major PITA. Taking the monorail from Contemporary (after valet parking) over to the MK took 25 minutes. I only did it the once because my kids wanted to ride the monorail. If efficiency is your goal, definitely valet park and walk. For me, it was worth the extra $18 a day - added bonus NO CROWDS on the walk-way (it seems as though very few people walk).