I disagree, Santorini is a tourist trap as long as you get fooled and not choose wisely where to eat, what to do. Santorini is known for the views and romance.
4 days in Athens is really good. Old Town is a must, trying Greek food is a must again. Plus, you have the advantage that they have many good options for fish/seafood (I had the best ever fried calamari/squid in Athens).