I don't think so. It is beacuse most of the famous attraction are very close to each other. The taxi fare is not so expensive in this case. And, the city's subway could take you around the city quickly, just for 2yuan/person/time. As for hiring a car just around the downtown area, you have to pay for 500yuan per 8 hours at least. Seems not a good idea! But you could hire a car to take you 5 to the Great Wall for a round-trip.