Harden my dirt parking spots
What is the soil type in this area? If the soil is sandy, it will not turn to mud when wet. A layer of the right kind of gravel might be both functional and pleasing to the eye, but don't put just anything down. Look around at what are others doing.

Parking cars on a bed of pine needles sounds to me like it would be a fire risk (catalytic converters get very hot). Ask the fire control authorities about whether the pine needles should be raked away from the car parking area.