As already noted, it makes no sense to drive to the MK when the Disney bus drops you off near the entrance. All the parking lots at WDW are huge so unless you get there early you would likely need to take a tram to the park entrance. Again, the Disney buses will leave you near all the park entrances. There is direct service to all the theme parks from all Disney resorts. The only service not available is direct resort to resort. If you plan on eating at a Disney resort simply plan on the nearest theme park for that part of the day. From the MK you can walk to the Contemporary or monorail to that resort as well as the Poly and the Grand Floridian. From the Disney Studios and the Epcot International Gateway you can walk or boat over to the Epcot resorts of Boardwalk, Yacht Club, Beach Club and Swan and Dolphin. There are many great restaurants in the Epcot resort area.
We have not rented a car in many years for our trips to WDW. Disney does a great job in getting people around. If you try to leave any park at closing it will be crowded, even with the extra buses they put in service. Best advice is to walk around, shop, eat, just take your time instead of trying to exit with everyone else. This is true if you take Disney transportation or drive. I cannot imagine trying to drive out with hundreds or more people trying to do the same at park closing. Last June my DS and I watched Wishes and then sat on a bench across from the castle for about 15-20 minutes as the hordes poured down Main Street. Then we slowly walked out of the park and to a quiet and empty bus station. Relax, take your time. Disney will take you anywhere you want to go without the hassle and expense of a rental car....and gasoline!