Although most of Greek popularity live an agony about how their future will be affected by the decisions of the new government, you will stay unaffected by all these – tourists have never been a target.
Even if Greece exits the Euro, and reinstates the Drachma, that will have minor effect to your vacation. You will still be able to make payments as before and probably prices will be lower than usual. Either currency changes or not, surely prices at hotels, tavernas and bars are lower compared to the prices before the economic crisis.
There may be some demonstrations in Athens, Syntagma square. You better avoid the area where demonstrations happen. Strikes may cause disruption to public transport. We advise you to be informed for any upcoming strikes that may affect your travel schedule. Taxis are everywhere, throughout the country. Ferry and bus services are rarely affected by strikes.