If you are a group of three or more you can book a personal tour with George the Famous Taxi Driver for about the same price and have a much richer experience than if you travel with a large group. But many of the travel agencies offer tours such as the 4-Day Classical Tour that visits the most popular mainland
While a car is not essential, it is certainly helpful, especially if you are traveling on your own. This is my ever-expanding Guide to the Greek Mainland. While most first time travelers go to the Greek Islands, many long-time visitors to Greece find that the Peloponnesos and the mainland maintain the traditional qualities they like most.