I work in travel publishing and our advice for Greece now is go. As long as you're prepared to be flexible, there's no reason to cancel a trip to the country.
If there are restrictions on ATM withdrawals (I don't think there ever were for tourists) or if smaller vendors aren't accepting credit cards, keep enough cash on you to get by. Real money is better than digital money right now if you're Greek.
Outside of the few spots of violence a month or so ago, there's nothing to worry about safety-wise, and even then the demonstrations were limited to Syntagma Square in Athens.
As always in travel, hope for the best but be flexible, smart and aware. The people and businesses you give your tourism money to will appreciate you haven't written off the whole country and you might have an even better experience than you expected.