Normally I would totally advocate staying close and being able to walk. However, you are only going one day, so I can see how the staying close isn't quite as vital. Here are the things to consider. Will you get up extra early in the morning for your one Disney day? Do you plan on staying in the park from 8AM-midnight or 9AM-11PM, whatever the hours may be? Are you the type of person who absolutely needs time away from the people, noise, and hubbub of the parks in the middle of the day to recharge? Are you able to "travel light", i.e. fit your needs for the day into one or two backpacks to either carry or stash in a locker, or are you the type who needs to go back to the hotel for a snack, a sweatshirt, a change of clothes or shoes, etc.?
If you stay at a non-walking distance hotel, you need to be prepared to arrive very early, well before park opening and possibly walk from the parking structure to the park rather than waiting for the shuttle. You will lose too much time driving back to your hotel and back to the park during the middle of the day, so you need to take "breaks" by sitting on benches and people-watching, going to a meal, going to a show, visiting Downtown Disney for an hour, trying out one of the chairs in the lobby of the Grand, and so on. You need to carry with you only what you are most likely to need during the day; if it's more than you want to constantly lug around, there's always the possibility of a locker. If you stay for the fireworks, stick around in the parks at least 30-60 minutes afterwards so you're not leaving with the main crush of people. Even then don't be surprised if you can't just hop on a shuttle back to the parking lot, so be of the mindset that you might have to walk or wait.
We have only driven to the park a couple of times, but those were for quick one-shots such as yours. These were not "un-busy" times since they were Columbus Day weekends during Halloweentime in 2009 and 2007. The key was to get there early, be patient, and be willing to do things a little more commando style than we are used to. We found that it was easy enough to manage though because it's the duration that gets us eventually. We are way more tired staying across the street and taking breaks but visiting 3 days in a row than we were driving in and out and not getting a real break for one day.