The boat trip to Shipwreck's beach is basically tourist trap. There will be about 50-100 people travelling with you and you will not be able to see much from a boat on a way there. Our boat did not stop on a beach at all due to bad weather and water conditions.
Plus, it is not very spectacular view from a beach, as it looks on pictures. The food and drinks on a boat are really overpriced a lot. The swimming from a boat was not very fantastic either, as water was quite cold. Also, we were very cold on a boat due to strong sea wind, everyone had to cover themselves with towels.
Unique Suggestions: Take plenty of water and drinks, if it is possible, as you will have to pay 2.5 euros for tiny drink (tea, cola, other drinks), take your own food if you budget is not very large. Also, you will be able to buy some more water, drinks when a boat will stop on a beach for a lunch, but it will be after a few hours of travelling.
Prepare to pay about 15-20 euros as minimum per person for a luch (not included in a tour price). I have found my lunch at the restaurant a bit small after spending all day on a boat, for a main course (8 euros) I had only 2 small oven baked peppers on a plate.
Fun Alternatives: It is best to see Shipwreck from above - take a coach/ car tour there.
I also vote this as a must see, but be aware that every one else also wants to go and see the Shipwreck.
Unique Suggestions: Many boats arrive at the same time and it is a mad scramble to the shore if you only have an hour there dont bother taking a towel to sit down on as there will probably not be enough room to do this!!
Fun Alternatives: Take a small cruiser, thet seem to go early morning to miss the crowds