Got money? Cuz one thing to do would be hire the car service with driver from the Aerocity website, and have him take you all over, have your luggage in the car, etc!! Maybe you could negotiate a good three hr price. But I like the idea of the metro. If you plan the walk as some have suggested-- opera, plaza mayor, sol, paseo del prado etc. you can see the highlights and then zip back out to the airport.