We have been to Aghia Efimia twice this year and it was great both times. The first time, we booked a villa before we went which was very expensive (on the main road out of Aghia and too noisy), but the second time (last week) we just turned up and got an appartment overlooking the harbour for 30 euros a night.
If you go in August it is packed full so you would have to book beforehand.
The cost of a taxi from the airport is 40 euros but agree this with the driver before the journey! Ask one of the car hire offices in Aghia to book a taxi for the return to the airport and they will tell the taxi that it is 40 euros!
There are enough restaurants to eat somewhere new each night. The ones with lots of people eating in are not always the best!
From the harbour you can hire a boat and get a ferry to Ithica.
Might see you there.