Resort parking is not intended for park access. So, if you eat at a resort, you are expected to move your car to the desired park's parking lot when you finish eating.
You may leave your car there if you pay to valet park.
Do people park at, say, BC, and eat and then head to Epcot for the day? Sure they do. And most of the time people get away with it. But, here's the thing...if you're intent on doing this? Please be considerate of those paying the high rates to stay at that resort and park in a distant parking spot if you're going to leave the car. Try not to take a close spot...just more polite to allow those staying at the resort to use those spots.
I really wish Disney would institute a keyed entry system for some of the resort lots. They could leave a distant area open to those who are using the facilities but that would enable those staying at the resort to continue using the near to resort spots.