Your reasonable question actually opens a huge can of worms. One issue is whether such a low daily quote indicates a company that makes money from Extras and will engineer it so that you really have to take the Extras. Many companies, big and small, now demand written proof of non-Their Own insurance. Did they offer an option to cover the 600 Euros? Nowadays there are often a host of CDW options, with separate charges for wheels and tires, glass and windshields, even for swapping of the car if it breaks down!!!! Do you have collision insurance on your home car? Does it cover every car you drive if it should be needed? Would you WANT to make a claim against it if it increases your rates at home for the next five years? Are you over 25?
I've never driven in Greece, but last time I was there people in Athens parked on the sidewalk. That indicates to me a sort of Wild West of driving (another example is Naples, Italy.) How little coverage do you feel comfortable with?
Edit: You write later that you've never caused damage to a car in Greece. Isn't a major reason for CDW what other people might do? Even in a parking area when your car is not moving or occupied?
But since you have indicated that you only want the answer to specific question, I would say that a 600 Euro deductible gives the rental company no incentive to overlook the tiniest blemish they might find when you return the car. No, I don't recommend a CDW that only protects you against financial catastrophe, but not against normal risks of car usage.