I spent a week based in Agios Nikolaus about 10 years ago. It is a beautiful village around the harbour. At the time, went with Greece Direct.
The harbour is pretty much the only focal point, tavernas around it and nearby served ok food, but never ate anything outstanding there. There was at least one 'gift shop' which reduced the charm somewhat.
On a daily basis, a little fish sale happened (I think preceded by a ringing bell). the term little can be taken in two ways, there were not many sellers and what they usually sold was pretty small - not like what can be seen at Tasomanolis for example. Despite the abundance of the famous Kalamata olives, the oils produced are nothing like the ones found in Plakias.
Despite extensive sea frontage close to the village centre, the nearest beach is between 1/2 and 1 mile along the road to the East, it is small but was then not overly busy, this may have changed of course now. There was from memory at least one taverna next to the beach. The beach shelved fairly dramatically into the water. The best local place for swimming was a rocky area just on the edge of the village, complete with a little church cut into the rocks, the water was well over 3 metres deep, though there were small channels in the rocks that could be paddled - beware of sea urchins there though!
Nearby places - the bigger resort of Stoupa, with larger beach, pedalos and a larger selection of eateries/drinkeries/hotels (still not a huge place), this is reachable by local bus and was I think about 10-20 minutes away. If you are up for hiring a car then further afield you will find the ancient abandoned hill town Mystras and if you take the correct route back you could make a stop off at the beautiful village of Limani with a perfect waterside taverna.
As I said it is some years since I was there, it is a beautiful part of greece and may well have experienced the same kind of expansion Plakias has seen in the intervening time.