I used to dismiss the lighthouse until the day I was beaten to another wonder and had to build it. Now it's my favourite and I almost restart the game if I can't get it. I usually play large continent maps with 12 civs on PTW. I also use the 0-research strategy from the first turn, buying techs from other civs instead of researching them myself.
Not only do the ships get another movement point, The Lighthouse also enables them to stay safely on sea squares. This brings benefits such as:
-instead of going 1 square out from coast and back, you can begin at a sea square, go 2 squares into the ocean and back.
-when your ships are on sea squares, they will not be attacked by barbarian galleys, and probably not by enemy ships either (never happened to me).
- you will get a larger world and territory maps that can be used for trading
- you will get to the small islands not adjacent to the coast first and can settle them first.
- a corrupt city on a remote arctic island wont produce much, but it makes your empire larger. Your ROP deals will be better and think about how many ROP deals you will sign (and renegotiate) with 12 civs from that point to the end of the game. That's a major effect.
- all the arctic islands will ensure you get oil later on, and other resources as well.
- you might reach the other continent first (I usually get 2 continents) and now you can soon trade contacts with 5-6 civs unknown to your neighbours.