Do you really need a travel guide? Ask yourself what you are looking for from a guide.

People often expect to get info on hotels and restaurants. Frankly, using a guide for that in Greece seems like a waste of money and time. Just get off the ferry landing or train station and look around - you can probably see 5 hotels and 8 places to eat from there. In any case, these business go in and out of existence and in and out of favor so fast that a book can only give you a general guide. There must be 50-75 hotels in the Plaka area of Athens alone, and I've never seen a guide list more than 5 or 10. And it isn't as if they list the best 5 or 10 either.

Where guides could be useful to you is in pointing you to things to see - especially those not on someone's top ten list. Guides can also help just to show you the physical layout of a place, and provide maps. I would have expected guides to be helpful with "practicalities": how to get on the ferry, money changing issues, etc. Often they only say vague things about these topics.