Dont go on organised tour, walk (10 mins) out of the Port towards the train station and get a train. It costs less than 3Euro for 2 people return. 5mins from stop to Acropoli.
Yes we did in 2006...sightseeing was fine, we did an excursion around the main sights then to the Plaka area for souvenir type shops which were all open in the morning...don't know about the afternoon tho'..I should imagine it was better on a Sunday because there was no 'going to work' traffic.
This website lists what is open :http://www.athensinfoguide.com/open.ht.